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Acute chorioamnionitis and funisitis: definition, pathologic features, and clinical significance

  • Chong Jai Kim
    Affiliations
    Department of Pathology, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea

    Perinatology Research Branch, Program for Perinatal Research and Obstetrics, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD and Detroit, MI
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  • Roberto Romero
    Correspondence
    Corresponding author: Roberto Romero, MD, DMedSc.
    Affiliations
    Perinatology Research Branch, Program for Perinatal Research and Obstetrics, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD and Detroit, MI

    Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, MI

    Department of Epidemiology and Biostatistics, Michigan State University, East Lansing, MI

    Center for Molecular Medicine and Genetics, Wayne State University, Detroit, MI
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  • Piya Chaemsaithong
    Affiliations
    Perinatology Research Branch, Program for Perinatal Research and Obstetrics, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD and Detroit, MI

    Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, MI
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  • Noppadol Chaiyasit
    Affiliations
    Perinatology Research Branch, Program for Perinatal Research and Obstetrics, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD and Detroit, MI

    Department of Obstetrics and Gynecology, Wayne State University School of Medicine, Detroit, MI
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  • Bo Hyun Yoon
    Affiliations
    Perinatology Research Branch, Program for Perinatal Research and Obstetrics, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD and Detroit, MI

    Department of Obstetrics and Gynecology, Seoul National University College of Medicine, Seoul, Korea
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  • Yeon Mee Kim
    Affiliations
    Perinatology Research Branch, Program for Perinatal Research and Obstetrics, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, Bethesda, MD and Detroit, MI

    Department of Pathology, Haeundae Paik Hospital, Inje University College of Medicine, Busan, Korea
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      Acute inflammatory lesions of the placenta consist of diffuse infiltration of neutrophils at different sites in the organ. These lesions include acute chorioamnionitis, funisitis, and chorionic vasculitis and represent a host response (maternal or fetal) to a chemotactic gradient in the amniotic cavity. While acute chorioamnionitis is evidence of a maternal host response, funisitis and chorionic vasculitis represent fetal inflammatory responses. Intraamniotic infection generally has been considered to be the cause of acute chorioamnionitis and funisitis; however, recent evidence indicates that “sterile” intraamniotic inflammation, which occurs in the absence of demonstrable microorganisms induced by “danger signals,” is frequently associated with these lesions. In the context of intraamniotic infection, chemokines (such as interleukin-8 and granulocyte chemotactic protein) establish a gradient that favors the migration of neutrophils from the maternal or fetal circulation into the chorioamniotic membranes or umbilical cord, respectively. Danger signals that are released during the course of cellular stress or cell death can also induce the release of neutrophil chemokines. The prevalence of chorioamnionitis is a function of gestational age at birth, and present in 3–5% of term placentas and in 94% of pacentas delivered at 21-24 weeks of gestation. The frequency is higher in patients with spontaneous labor, preterm labor, clinical chorioamnionitis (preterm or term), or ruptured membranes. Funisitis and chorionic vasculitis are the hallmarks of the fetal inflammatory response syndrome, a condition characterized by an elevation in the fetal plasma concentration of interleukin-6, and associated with the impending onset of preterm labor, a higher rate of neonatal morbidity (after adjustment for gestational age), and multiorgan fetal involvement. This syndrome is the counterpart of the systemic inflammatory response syndrome in adults: a risk factor for short- and long-term complications (ie, sterile inflammation in fetuses, neonatal sepsis, bronchopulmonary dysplasia, periventricular leukomalacia, and cerebral palsy). This article reviews the definition, pathogenesis, grading and staging, and clinical significance of the most common lesions in placental disease. Illustrations of the lesions and diagrams of the mechanisms of disease are provided.

      Key words

      Acute chorioamnionitis is the most frequent diagnosis in placental pathology reports and is generally considered to represent the presence of intraamniotic infection or “amniotic fluid infection syndrome.”
      • Blanc W.A.
      Amniotic infection syndrome; pathogenesis, morphology, and significance in circumnatal mortality.
      • Russell P.
      Inflammatory lesions of the human placenta: clinical significance of acute chorioamnionitis.
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      Pathology of the placenta and cord in ascending and in haematogenous infection.
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      • Eschenbach D.A.
      A case-control study of chorioamnionic infection and histologic chorioamnionitis in prematurity.

      Benirschke K, Burton GJ, Baergen RN, eds. Infectious diseases. In: Pathology of the human placenta, 6th ed. Berlin: Springer; 2012:557-656.

      Fox H, Sebire NJ. Infections and inflammatory lesions of the placenta. In: Pathology of the placenta, 3d ed. China: Elsevier; 2007:303-54.

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      The relationship between acute inflammatory lesions of the preterm placenta and amniotic fluid microbiology.
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      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      • Redline R.W.
      Placental inflammation.
      Yet, acute chorioamnionitis can occur in the setting of “sterile intraamniotic inflammation” in the absence of demonstrable microorganisms and is induced by “danger signals” released under conditions of cellular stress, injury, or death.
      • Romero R.
      • Miranda J.
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      • et al.
      A novel molecular microbiologic technique for the rapid diagnosis of microbial invasion of the amniotic cavity and intra-amniotic infection in preterm labor with intact membranes.
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      Prevalence and clinical significance of sterile intra-amniotic inflammation in patients with preterm labor and intact membranes.
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      Sterile and microbial-associated intra-amniotic inflammation in preterm prelabor rupture of membranes.
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      Sterile intra-amniotic inflammation in asymptomatic patients with a sonographic short cervix: prevalence and clinical significance.
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      Clinical chorioamnionitis at term I: microbiology of the amniotic cavity using cultivation and molecular techniques.
      Therefore, acute chorioamnionitis is evidence of intraamniotic inflammation and not necessarily intraamniotic infection. The characteristic morphologic feature of acute chorioamnionitis is diffuse infiltration of neutrophils into the chorioamniotic membranes.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      Since obstetricians use the term chorioamnionitis to refer to a clinical syndrome (the combination of fever, maternal or fetal tachycardia, uterine tenderness, foul-smelling amniotic fluid) frequently associated with “acute chorioamnionitis” on microscopic examination of the placenta, the word histologic has been introduced into the medical lexicon to specify the differences between the clinical syndrome, clinical chorioamnionitis, and the pathologic diagnosis of acute chorioamnionitis. These terms are not synonymous, and confusion occurs when they are used interchangeably. Herein, the term acute chorioamnionitis will refer to “acute histologic chorioamnionitis” given the focus of this article is the pathologic condition rather than the clinical syndrome. We will review the acute inflammatory responses deployed by the mother and fetus in response to inflammatory stimuli within the amniotic cavity.

      Definition

      The placenta is composed of three major structures: the placental disc, the chorioamniotic membranes, and the umbilical cord (Figure 1). Acute inflammatory lesions of the placenta are characterized by the infiltration of neutrophils in any of these structures.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      Specifically, when the inflammatory process affects the chorion and amnion, this is termed acute chorioamnionitis
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      ; if it affects the villous tree, this represents acute villitis.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      If the inflammatory process involves the umbilical cord (umbilical vein, umbilical artery, and the Wharton’s jelly), this is referred to as acute funisitis, the histologic counterpart of the fetal inflammatory response syndrome (FIRS; Figure 1).
      • Pacora P.
      • Chaiworapongsa T.
      • Maymon E.
      • et al.
      Funisitis and chorionic vasculitis: the histological counterpart of the fetal inflammatory response syndrome.
      Figure thumbnail gr1
      Figure 1The anatomy of the pregnant uterus with an emphasis on the placenta
      Modified from Benirschke K, et al.

      Benirschke K, Burton GJ, Baergen RN, eds. Infectious diseases. In: Pathology of the human placenta, 6th ed. Berlin: Springer; 2012:557-656.

      Infectious disease. In: Pathology of the human placenta, 6th ed. Berlin: Springer, 2012, 33.
      The left side of the illustration shows the fetus, umbilical cord, and placenta. The chorioamniotic membranes include the amnion and chorion. Decidua is the pregnant endometrium. The right side of the illustration shows a cross-section of the human placenta, which includes the chorionic plate, chorioamniotic membranes, umbilical cord, and the intervillous space. The basal plate of the placenta is traversed by the spiral arteries, which bring maternal blood into the intervillous space. The villous circulation (fetal) is illustrated in a cross-section of the stem villi. The fetal vessels on the surface of the chorionic plate include arteries and veins, which coalesce to form the umbilical vein and umbilical arteries.
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.

      Prevalence of acute chorioamnionitis

      Table 1 shows the frequency of acute chorioamnionitis as a function of gestational age at delivery in a study of 7505 placentas from singleton pregnancies that were delivered after 20 weeks of gestation.
      • Russell P.
      Inflammatory lesions of the human placenta: clinical significance of acute chorioamnionitis.
      It is noteworthy that the frequency of acute chorioamnionitis in patients who delivered between 21-24 weeks of gestation was 94.4% (17/18 patients).
      • Russell P.
      Inflammatory lesions of the human placenta: clinical significance of acute chorioamnionitis.
      This is consistent with multiple studies subsequently reported by our group
      • Lee S.M.
      • Park J.W.
      • Kim B.J.
      • et al.
      Acute histologic chorioamnionitis is a risk factor for adverse neonatal outcome in late preterm birth after preterm premature rupture of membranes.
      and others
      • Srinivas S.K.
      • Ma Y.
      • Sammel M.D.
      • et al.
      Placental inflammation and viral infection are implicated in second trimester loss.
      • Van Hoeven K.H.
      • Anyaegbunam A.
      • Hochster H.
      • et al.
      Clinical significance of increasing histologic severity of acute inflammation in the fetal membranes and umbilical cord.
      • Srinivas S.K.
      • Ernst L.M.
      • Edlow A.G.
      • Elovitz M.A.
      Can placental pathology explain second-trimester pregnancy loss and subsequent pregnancy outcomes?.
      and emphasizes the role of acute inflammation in early preterm deliveries and midtrimester spontaneous abortions.
      Table 1Frequency of chorioamnionitis according to gestational age at delivery
      Modified from Russell P.
      • Russell P.
      Inflammatory lesions of the human placenta: clinical significance of acute chorioamnionitis.
      Weeks of gestationChorioamnionitis, nTotal no. of patientsPercentage
      21–24171894.4
      25–28194839.6
      29–32349635.4
      33–365349710.7
      37–4023361393.8
      41–44367075.1
      Totals39275055.2
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.
      Acute chorioamnionitis is observed more frequently in the placentas of women who delivered after spontaneous labor at term than in the absence of labor
      • Seong H.S.
      • Lee S.E.
      • Kang J.H.
      • Romero R.
      • Yoon B.H.
      The frequency of microbial invasion of the amniotic cavity and histologic chorioamnionitis in women at term with intact membranes in the presence or absence of labor.
      • Park H.S.
      • Romero R.
      • Lee S.M.
      • Park C.W.
      • Jun J.K.
      • Yoon B.H.
      Histologic chorioamnionitis is more common after spontaneous labor than after induced labor at term.
      (early labor with cervical dilation of <4 cm, 11.6% [10/86] vs no labor, 4.4% [34/775]; P < .01).
      • Park H.S.
      • Romero R.
      • Lee S.M.
      • Park C.W.
      • Jun J.K.
      • Yoon B.H.
      Histologic chorioamnionitis is more common after spontaneous labor than after induced labor at term.
      Moreover, the longer the duration of labor and cervical dilation of >4 cm, the higher the frequency of acute chorioamnionitis (active labor, 30.4% [7/23] vs early labor, 11.6% [10/86]; P < .05).
      • Lee S.M.
      • Lee K.A.
      • Kim S.M.
      • Park C.W.
      • Yoon B.H.
      The risk of intra-amniotic infection, inflammation and histologic chorioamnionitis in term pregnant women with intact membranes and labor.
      This observation has two possible explanations: first, the frequency of microbial invasion of the amniotic cavity is higher in women in spontaneous labor at term with intact membranes than in those without labor (17% vs 1.5%).
      • Romero R.
      • Nores J.
      • Mazor M.
      • et al.
      Microbial invasion of the amniotic cavity during term labor: prevalence and clinical significance.
      Alternatively, labor per se is an inflammatory state, as demonstrated by the study of the gene expression profile of the chorioamniotic membranes.
      • Haddad R.
      • Tromp G.
      • Kuivaniemi H.
      • et al.
      Human spontaneous labor without histologic chorioamnionitis is characterized by an acute inflammation gene expression signature.
      The chorioamniotic membranes obtained from women who experienced labor (even in the absence of any detectable acute chorioamnionitis) overexpressed neutrophil-specific chemokines (chemokine [C-X-C motif] ligand 1 [CXCL1], CXCL2, and interleukin [IL]-8) and monocyte-specific chemokines (C-C motif ligand 3 [CCL3], macrophage inflammatory protein [MIP]-1α, CCL4 [MIP-1β], and CCL20 [MIP-3α]; Figure 2).
      • Haddad R.
      • Tromp G.
      • Kuivaniemi H.
      • et al.
      Human spontaneous labor without histologic chorioamnionitis is characterized by an acute inflammation gene expression signature.
      This is consistent with reports that the amniotic fluid concentrations of chemokines such as IL-8,
      • Romero R.
      • Ceska M.
      • Avila C.
      • Mazor M.
      • Behnke E.
      • Lindley I.
      Neutrophil attractant/activating peptide-1/interleukin-8 in term and preterm parturition.
      monocyte chemotactic protein (MCP)-1,
      • Esplin M.S.
      • Romero R.
      • Chaiworapongsa T.
      • et al.
      Amniotic fluid levels of immunoreactive monocyte chemotactic protein-1 increase during term parturition.
      growth-regulated oncogene (GRO)-α,
      • Cohen J.
      • Ghezzi F.
      • Romero R.
      • et al.
      GRO alpha in the fetomaternal and amniotic fluid compartments during pregnancy and parturition.
      MIP-1α,
      • Romero R.
      • Gomez R.
      • Galasso M.
      • et al.
      Macrophage inflammatory protein-1 alpha in term and preterm parturition: effect of microbial invasion of the amniotic cavity.
      and cytokines such as IL-1
      • Romero R.
      • Parvizi S.T.
      • Oyarzun E.
      • et al.
      Amniotic fluid interleukin-1 in spontaneous labor at term.
      • Romero R.
      • Brody D.T.
      • Oyarzun E.
      • et al.
      Infection and labor: III, interleukin-1: a signal for the onset of parturition.
      • Romero R.
      • Mazor M.
      • Brandt F.
      • et al.
      Interleukin-1 alpha and interleukin-1 beta in preterm and term human parturition.
      and IL-6
      • Gomez R.
      • Romero R.
      • Galasso M.
      • Behnke E.
      • Insunza A.
      • Cotton D.B.
      The value of amniotic fluid interleukin-6, white blood cell count, and gram stain in the diagnosis of microbial invasion of the amniotic cavity in patients at term.
      • Cox S.M.
      • Casey M.L.
      • MacDonald P.C.
      Accumulation of interleukin-1beta and interleukin-6 in amniotic fluid: a sequela of labour at term and preterm.
      are higher in women at term in spontaneous labor than in those not in labor.
      Figure thumbnail gr2
      Figure 2Spontaneous labor at term is an inflammatory phenomenon
      Modified from Figure 2 in Haddad R, et al.
      • Haddad R.
      • Tromp G.
      • Kuivaniemi H.
      • et al.
      Human spontaneous labor without histologic chorioamnionitis is characterized by an acute inflammation gene expression signature.
      The gene expression (mRNA) profile of the chorioamniotic membranes of women not in labor at term was compared to that of membranes obtained from women who had undergone labor. Patients with histologic inflammation of the amnion and chorion were excluded. The figure represents hierarchical clustering in which patients not in labor are labeled as “TNL” (black letters at the top of the figure), while those in labor are labeled as “TIL” (red letters at the top of the figure). Columns correspond to patients; rows correspond to the most discriminant microarray probe sets. The magnitude of expression changes (fold change) are coded in the color key. Most of the differentially-expressed genes shown in the figure are involved in inflammation (chemokines, cytokines). This is evidence that examining global gene expression (unbiased) indicates that inflammation-related molecules are overexpressed in labor.
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.

      Pathology

      The placenta is considered to be the apposition or fusion of the fetal membranes/placental disc to the uterine mucosa (decidua) for physiologic exchange.
      • Mossman H.W.
      Classics revisited: comparative morphogenesis of the fetal membranes and accessory uterine structures.
      The decidua is of maternal origin; the chorioamniotic membranes and villous tree are of fetal origin. Thus, the precise origin of the inflammatory process (maternal vs fetal) can be determined by whether infiltrating neutrophils are of maternal or fetal origin.
      Neutrophils are not normally present in the chorioamniotic membranes and migrate from the decidua into the membranes in cases of acute chorioamnionitis (Figure 3).
      • Mcnamara M.F.
      • Wallis T.
      • Qureshi F.
      • Jacques S.M.
      • Gonik B.
      Determining the maternal and fetal cellular immunologic contributions in preterm deliveries with clinical or subclinical chorioamnionitis.
      • Steel J.H.
      • O’Donoghue K.
      • Kennea N.L.
      • Sullivan M.H.
      • Edwards A.D.
      Maternal origin of inflammatory leukocytes in preterm fetal membranes, shown by fluorescence in situ hybridisation.
      On the other hand, maternal neutrophils normally circulate in the intervillous space (Figure 1). When there is a chemotactic gradient, neutrophils migrate toward the amniotic cavity, neutrophils in the intervillous space mobilize into the chorionic plate of the placenta, which is normally devoid of these cells. Thus, inflammation of the chorionic plate, except chorionic vasculitis, is also a maternal inflammatory response.
      Figure thumbnail gr3
      Figure 3Migration of the neutrophils from the decidual vessels into the chorioamniotic membranes
      A, Normal histology of the chorioamniotic membranes, which are composed of amnion and chorion laeve. The decidua is adjacent to the chorion and contains maternal capillaries (black asterisks). Neutrophils migrate from the maternal circulation in the presence of chemotactic gradient (increased amniotic fluid neutrophil chemokine concentrations). B, Migration of neutrophils from the decidual vessels (red) towards the amnion (indicated by upward-pointing arrows). The location of bacteria is within the amniotic cavity. Initially, neutrophils are in the decidua (left); however, in subsequent stages, invade the chorion (center) and amnion (right).
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.
      Neutrophils in acute chorioamnionitis are of maternal origin. Fluorescence in situ hybridization (FISH) with probes for X and Y chromosomes performed in cytospin slides of placentas from male fetuses showed that approximately 90% of neutrophils derived from the membranes were of maternal origin.
      • Mcnamara M.F.
      • Wallis T.
      • Qureshi F.
      • Jacques S.M.
      • Gonik B.
      Determining the maternal and fetal cellular immunologic contributions in preterm deliveries with clinical or subclinical chorioamnionitis.
      Subsequently, FISH combined with immunohistochemistry for CD45 (to identify leukocytes) demonstrated that CD45 positive cells in the chorionic membranes were of maternal origin.
      • Steel J.H.
      • O’Donoghue K.
      • Kennea N.L.
      • Sullivan M.H.
      • Edwards A.D.
      Maternal origin of inflammatory leukocytes in preterm fetal membranes, shown by fluorescence in situ hybridisation.
      In contrast, inflammation of the umbilical cord and the chorionic vessels on the chorionic plate of the placenta is of fetal origin.
      • Lee S.D.
      • Kim M.R.
      • Hwang P.G.
      • Shim S.S.
      • Yoon B.H.
      • Kim C.J.
      Chorionic plate vessels as an origin of amniotic fluid neutrophils.
      This conclusion is largely based on the understanding of the anatomy of these tissues, because neutrophils invading the walls of the umbilical vein and arteries must migrate from the fetal circulation to enter the walls of these vessels (Figure 4). Insofar as the origin of white blood cells in the amniotic fluid in cases of intraamniotic inflammation, the only study reported to date for cases of intrauterine infection with intact membranes suggested that 99% of neutrophils are of fetal origin.
      • Sampson J.E.
      • Theve R.P.
      • Blatman R.N.
      • et al.
      Fetal origin of amniotic fluid polymorphonuclear leukocytes.
      Figure thumbnail gr4
      Figure 4Topography of the inflammatory process in the umbilical cord
      A, Typically, acute funisitis begins as inflammation of the umbilical vein (umbilical phlebitis; the red vessel represents the umbilical vein), followed by umbilical arteritis involving the umbilical arteries (blue). B, Progression of inflammation along the length of the umbilical cord. The initial phase is multifocal, as demonstrated by the yellow/orange rings in the second umbilical cord from left to right. Subsequently, the areas of inflammation coalesce, and funisitis affects the entire umbilical cord.
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.
      Inflammation of the umbilical vessels begins in the vein (phlebitis) and is followed by involvement of the arteries (arteritis). Infiltration of neutrophilis into the Wharton's jelly is common in acute funisitis.
      • Kim C.J.
      • Yoon B.H.
      • Kim M.
      • Park J.O.
      • Cho S.Y.
      • Chi J.G.
      Histo-topographic distribution of acute inflammation of the human umbilical cord.
      The molecular pathogenesis of funisitis has been studied with the use of microarray analysis followed by quantitative real-time polymerase chain reaction (PCR) obtained from micro-dissected umbilical arteries and veins. The expression of IL-8 messenger RNA (mRNA; the prototypic neutrophil chemokine) is higher in the umbilical vein than in the umbilical artery.
      • Kim C.J.
      • Yoon B.H.
      • Kim M.
      • Park J.O.
      • Cho S.Y.
      • Chi J.G.
      Histo-topographic distribution of acute inflammation of the human umbilical cord.
      Moreover, there are substantial differences in the genes expressed by the walls of the umbilical artery and vein. The pattern of gene expression suggests that the wall of the umbilical vein is more prone to a proinflammatory response than that of the umbilical arteries.
      • Kim C.J.
      • Yoon B.H.
      • Kim M.
      • Park J.O.
      • Cho S.Y.
      • Chi J.G.
      Histo-topographic distribution of acute inflammation of the human umbilical cord.
      This explains why the umbilical vein is the first vessel to show inflammatory changes, and the presence of arteritis is evidence of a more advanced fetal inflammatory response.
      • Kim C.J.
      • Yoon B.H.
      • Kim M.
      • Park J.O.
      • Cho S.Y.
      • Chi J.G.
      Histo-topographic distribution of acute inflammation of the human umbilical cord.
      Indeed, the umbilical cord plasma concentrations of IL-6 (a cytokine used to define systemic inflammation) and the frequency of neonatal complications are higher in cases with umbilical arteritis than in those with only phlebitis.
      • Kim C.J.
      • Yoon B.H.
      • Romero R.
      • et al.
      Umbilical arteritis and phlebitis mark different stages of the fetal inflammatory response.
      Systematic studies of the umbilical cord suggest that acute funisitis begins as multiple, discrete foci along the umbilical cord, which then merge as the inflammatory process progresses.
      • Kim C.J.
      • Yoon B.H.
      • Kim M.
      • Park J.O.
      • Cho S.Y.
      • Chi J.G.
      Histo-topographic distribution of acute inflammation of the human umbilical cord.
       Figure 4 shows the topography of the inflammatory process in several umbilical cords that were sectioned serially at 1-mm intervals. The chemotactic gradient that attracted neutrophils from the lumen of the umbilical vessels into the Wharton’s jelly is thought to be an elevated concentration of chemokines in the amniotic fluid. The severity of funisitis correlates with fetal plasma IL-6 concentrations (an indicator of the severity of the systemic fetal inflammatory response) and amniotic fluid IL-6; the latter reflects the intensity of the intraamniotic inflammatory response.
      • Kim C.J.
      • Yoon B.H.
      • Romero R.
      • et al.
      Umbilical arteritis and phlebitis mark different stages of the fetal inflammatory response.

      Histologic grading and staging of acute chorioamnionitis

      Several grading and staging systems have been proposed to describe the severity of acute chorioamnionitis.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      • Van Hoeven K.H.
      • Anyaegbunam A.
      • Hochster H.
      • et al.
      Clinical significance of increasing histologic severity of acute inflammation in the fetal membranes and umbilical cord.
      • Salafia C.M.
      • Weigl C.
      • Silberman L.
      The prevalence and distribution of acute placental inflammation in uncomplicated term pregnancies.
      • Yoon B.H.
      • Romero R.
      • Kim C.J.
      • et al.
      Amniotic fluid interleukin-6: a sensitive test for antenatal diagnosis of acute inflammatory lesions of preterm placenta and prediction of perinatal morbidity.
      • Miyano A.
      • Miyamichi T.
      • Nakayama M.
      • Kitajima H.
      • Shimizu A.
      Differences among acute, subacute, and chronic chorioamnionitis based on levels of inflammation-associated proteins in cord blood.
      • Ohyama M.
      • Itani Y.
      • Yamanaka M.
      • et al.
      Re-evaluation of chorioamnionitis and funisitis with a special reference to subacute chorioamnionitis.
      • Andrews W.W.
      • Goldenberg R.L.
      • Faye-Petersen O.
      • Cliver S.
      • Goepfert A.R.
      • Hauth J.C.
      The Alabama Preterm Birth study: polymorphonuclear and mononuclear cell placental infiltrations, other markers of inflammation, and outcomes in 23- to 32-week preterm newborn infants.
      • Torricelli M.
      • Voltolini C.
      • Toti P.
      • et al.
      Histologic chorioamnionitis: different histologic features at different gestational ages.
      The most widely used system is that recommended by the Amniotic Fluid Infection Nosology Committee of the Perinatal Section of the Society for Pediatric Pathology and reported by Redline et al
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      in 2003. Although that article refers to the term amniotic fluid infection syndrome, it is now clear that these lesions do not always represent intraamniotic infection.
      Redline et al
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      classified acute inflammatory lesions of the placenta into two categories: maternal inflammatory response and fetal inflammatory response. The term stage refers to the progression of the process based on the anatomical regions infiltrated by neutrophils; the term grade refers to the intensity of the acute inflammatory process at a particular site.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      In the context of a maternal inflammatory response, a stage 1 lesion is characterized by the presence of neutrophils in the chorion or subchorionic space; stage 2 refers to neutrophilic infiltration of the chorionic connective tissue and/or amnion or the chorionic plate; and stage 3 is necrotizing chorioamnionitis with amnion epithelial necrosis.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      Grade 1 (mild to moderate) refers to individual or small clusters of maternal neutrophils that diffusely infiltrate the chorion laeve, chorionic plate, subchorionic fibrin, or amnion. Grade 2 (severe) consists of the presence of ≥3 chorionic microabscesses, which are defined as confluence of neutrophils measuring at least 10 × 20 cells.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      Microabscesses typically are located between the chorion and decidua and/or under the chorionic plate.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      Grade 2 is also applied in the presence of a continuous band of confluent neutrophils in the chorion of >10 cells in width that occupy more than one-half of the subchorionic fibrin or one revolution of the membrane roll. Other staging and grading systems have been used and subsequently modified.
      • Van Hoeven K.H.
      • Anyaegbunam A.
      • Hochster H.
      • et al.
      Clinical significance of increasing histologic severity of acute inflammation in the fetal membranes and umbilical cord.
      • Salafia C.M.
      • Weigl C.
      • Silberman L.
      The prevalence and distribution of acute placental inflammation in uncomplicated term pregnancies.
      • Yoon B.H.
      • Romero R.
      • Kim C.J.
      • et al.
      Amniotic fluid interleukin-6: a sensitive test for antenatal diagnosis of acute inflammatory lesions of preterm placenta and prediction of perinatal morbidity.
      • Miyano A.
      • Miyamichi T.
      • Nakayama M.
      • Kitajima H.
      • Shimizu A.
      Differences among acute, subacute, and chronic chorioamnionitis based on levels of inflammation-associated proteins in cord blood.
      • Ohyama M.
      • Itani Y.
      • Yamanaka M.
      • et al.
      Re-evaluation of chorioamnionitis and funisitis with a special reference to subacute chorioamnionitis.
      • Andrews W.W.
      • Goldenberg R.L.
      • Faye-Petersen O.
      • Cliver S.
      • Goepfert A.R.
      • Hauth J.C.
      The Alabama Preterm Birth study: polymorphonuclear and mononuclear cell placental infiltrations, other markers of inflammation, and outcomes in 23- to 32-week preterm newborn infants.
      • Torricelli M.
      • Voltolini C.
      • Toti P.
      • et al.
      Histologic chorioamnionitis: different histologic features at different gestational ages.
      Staging and grading are also applicable to the fetal inflammatory response.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      Staging (which refers to the location of neutrophil infiltration) is more important and reproducible than grading in the assessment of the severity of the inflammatory process.
      • Park C.W.
      • Yoon B.H.
      • Kim S.M.
      • Park J.S.
      • Jun J.K.
      Which is more important for the intensity of intra-amniotic inflammation between total grade or involved anatomical region in preterm gestations with acute histologic chorioamnionitis?.
      For example, involvement of the amnion (amnionitis) is associated with more intense fetal and intraamniotic inflammation (assessed by the concentration of cytokines) than involvement of the chorion alone.
      • Park C.W.
      • Moon K.C.
      • Park J.S.
      • Jun J.K.
      • Romero R.
      • Yoon B.H.
      The involvement of human amnion in histologic chorioamnionitis is an indicator that a fetal and an intra-amniotic inflammatory response is more likely and severe: clinical implications.
      The rates of funisitis and positive amniotic fluid culture for microorganisms and the median umbilical cord plasma C-reactive protein, median amniotic fluid matrix metalloproteinase (MMP)-8 concentration, and amniotic fluid white blood cell count are higher when the inflammatory process involves amnion and chorion than when neutrophil infiltration is restricted to the chorion/decidua
      • Park C.W.
      • Moon K.C.
      • Park J.S.
      • Jun J.K.
      • Romero R.
      • Yoon B.H.
      The involvement of human amnion in histologic chorioamnionitis is an indicator that a fetal and an intra-amniotic inflammatory response is more likely and severe: clinical implications.
      (Figures 5 and 6). Moreover, amniotic fluid MMP-8 concentration is correlated with the severity of acute chorioamnionitis (grading).
      • Kim S.M.
      • Romero R.
      • Park J.W.
      • Oh K.J.
      • Jun J.K.
      • Yoon B.H.
      The relationship between the intensity of intra-amniotic inflammation and the presence and severity of acute histologic chorioamnionitis in preterm gestation.
      Figure thumbnail gr5
      Figure 5Staging of acute chorioamnionitis
      Acute chorioamnionitis of the extraplacental chorioamniotic membranes: A, Normal chorioamniotic membranes shows the absence of neutrophils. B, Acute chorionitis is stage 1 acute inflammation of the chorioamniotic membranes, in which neutrophilic infiltration is limited to the chorion. C, Acute chorioamnionitis is stage 2 acute inflammation of the chorioamniotic membranes; neutrophilic migration into the amniotic connective tissue is shown (asterisk). D, Necrotizing chorioamnionitis is stage 3 acute inflammation of the chorioamniotic membranes, whose characteristic is the amnion epithelial necrosis (arrows). Acute inflammation of the chorionic plate: E, Acute subchorionitis, stage 1 acute inflammation shows neutrophils in the subchorionic fibrin in the chorionic plate (arrows). The area immediately below the arrows represents the intervillous space. F, Acute chorionic vasculitis (asterisk) is a stage 1 fetal inflammatory response. Acute inflammation of the chorioamniotic membranes (A-E) represents a maternal inflammatory response. Chorionic vasculitis is inflammation on the surface of the fetal vessels within the chorionic plate ( presents the anatomical location).
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.
      Figure thumbnail gr6
      Figure 6Staging of acute funisitis
      A, Umbilical phlebitis shows amniotropic migration of fetal neutrophils into the muscle layer of the umbilical vein. Umbilical phlebitis represents stage 1 fetal inflammation. B, Umbilical arteritis is a stage 2 fetal inflammatory response. C, Necrotizing funisitis is considered stage 3 fetal inflammatory response. Its characteristic feature is concentric, perivascular distribution of degenerated neutrophils (asterisk). The presence of a thrombus should be considered to be a severe fetal inflammatory response.
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.
      The reproducibility of the grading and staging of maternal and fetal inflammation has been subject of a rigorous study by Redline et al
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.
      ; 20 cases were reviewed by six pathologists who were asked to identify 12 inflammatory lesions. The kappa coefficient was used to measure agreement among observers. In general, the presence or absence of inflammation had a very high kappa value (0.93 for acute chorioamnionitis and 0.90 for acute chorioamnionitis/fetal inflammatory response). A kappa value between 0.81 and 1 is considered to represent almost perfect agreement. In contrast, the value of kappa was lower for the determination of grading and staging. The authors concluded that there is greater agreement among pathologists in identifying the presence or absence of inflammation, rather than in the assessment of grading and staging.
      • Redline R.W.
      • Faye-Petersen O.
      • Heller D.
      • Qureshi F.
      • Savell V.
      • Vogler C.
      Amniotic infection syndrome: nosology and reproducibility of placental reaction patterns.

      Pathways of microbial invasion of the amniotic cavity

      Under normal conditions, the amniotic cavity is sterile for microorganisms with the use of cultivation
      • Harris J.W.
      • Brown H.
      Bacterial content of the uterus at cesarean section.
      and molecular microbiologic techniques, based on the detection of the 16S ribosomal RNA (rRNA) gene (present in all bacteria, but not in mammalian cells). Four pathways have been proposed whereby microorganisms reach the amniotic cavity
      • Romero R.
      • Dey S.K.
      • Fisher S.J.
      Preterm labor: one syndrome, many causes.
      • Romero R.
      • Mazor M.
      Infection and preterm labor.
      • Romero R.
      • Mazor M.
      • Munoz H.
      • Gomez R.
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      • Sherer D.M.
      The preterm labor syndrome.
      • Goncalves L.F.
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      • Romero R.
      Intrauterine infection and prematurity.
      • Romero R.
      • Espinoza J.
      • Kusanovic J.P.
      • et al.
      The preterm parturition syndrome.
      : (1) ascending from the lower genital tract,
      • Blanc W.A.
      Amniotic infection syndrome; pathogenesis, morphology, and significance in circumnatal mortality.
      • Romero R.
      • Salafia C.M.
      • Athanassiadis A.P.
      • et al.
      The relationship between acute inflammatory lesions of the preterm placenta and amniotic fluid microbiology.
      • Benirschke K.
      Routes and types of infection in the fetus and the newborn.
      • Naeye R.L.
      • Dellinger W.S.
      • Blanc W.A.
      Fetal and maternal features of antenatal bacterial infections.
      (2) hematogenous,
      • Cunningham F.G.
      • Morris G.B.
      • Mickal A.
      Acute pyelonephritis of pregnancy: a clinical review.
      • Benedetti T.J.
      • Valle R.
      • Ledger W.J.
      Antepartum pneumonia in pregnancy.
      • Kaul A.K.
      • Khan S.
      • Martens M.G.
      • Crosson J.T.
      • Lupo V.R.
      • Kaul R.
      Experimental gestational pyelonephritis induces preterm births and low birth weights in C3H/HeJ mice.
      (3) accidental introduction at the time of amniocentesis, percutaneous umbilical cord blood sampling, fetoscopy, or another invasive procedure,
      • Romero R.
      • Jeanty P.
      • Hobbins J.C.
      Invasive techniques for antenatal diagnosis: Chorion villous biopsy, fetoscopy and amniocentesis in prenatal diagnosis.
      • Fray R.E.
      • Davis T.P.
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      Clostridium welchii infection after amniocentesis.
      • Romero R.
      • Jeanty P.
      • Reece E.A.
      • et al.
      Sonographically monitored amniocentesis to decrease intraoperative complications.

      Romero R, Hobbins JC, Mahoney MJ. Fetal blood sampling and fetoscopy. In: Aubrey Milunsky, editor. Genetic disorders of the fetus. New York, NY: Plenum Publishing 1986:571-98.

      • McColgin S.W.
      • Hess L.W.
      • Martin R.W.
      • Martin Jr., J.N.
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      Group B streptococcal sepsis and death in utero following funipuncture.
      • Hamoda H.
      • Chamberlain P.F.
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      • Li Kim Mui S.V.
      • Chitrit Y.
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      and (4) retrograde seeding from the fallopian tubes via the peritoneal cavity
      • Benirschke K.
      Routes and types of infection in the fetus and the newborn.
      However, there is limited evidence in support of the latter pathway.
      Ascending microbial invasion from the lower genital tract appears to be the most frequent pathway for intraamniotic infection (Figures 7 and 8).
      • Romero R.
      • Mazor M.
      Infection and preterm labor.
      Although all pregnant women have microorganisms in the lower genital tract, most do not have intraamniotic infection. The mucus plug represents an anatomic and functional barrier to ascending infection during pregnancy.
      • Hein M.
      • Helmig R.B.
      • Schonheyder H.C.
      • Ganz T.
      • Uldbjerg N.
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      • Hein M.
      • Valore E.V.
      • Helmig R.B.
      • Uldbjerg N.
      • Ganz T.
      Antimicrobial factors in the cervical mucus plug.
      • Habte H.H.
      • De Beer C.
      • Lotz Z.E.
      • et al.
      The inhibition of the human immunodeficiency virus type 1 activity by crude and purified human pregnancy plug mucus and mucins in an inhibition assay.
      • Becher N.
      • Adams Waldorf K.
      • Hein M.
      • Uldbjerg N.
      The cervical mucus plug: structured review of the literature.
      • Becher N.
      • Hein M.
      • Danielsen C.C.
      • Uldbjerg N.
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      • Lee D.C.
      • Hassan S.S.
      • Romero R.
      • et al.
      Protein profiling underscores immunological functions of uterine cervical mucus plug in human pregnancy.
      • Hansen L.K.
      • Becher N.
      • Bastholm S.
      • et al.
      The cervical mucus plug inhibits, but does not block, the passage of ascending bacteria from the vagina during pregnancy.
      In the nonpregnant state, the endometrial cavity is not sterile,
      • Romero R.
      • Espinoza J.
      • Mazor M.
      Can endometrial infection/inflammation explain implantation failure, spontaneous abortion, and preterm birth after in vitro fertilization?.
      • Espinoza J.
      • Erez O.
      • Romero R.
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      • Mitchell C.M.
      • Haick A.
      • Nkwopara E.
      • et al.
      Colonization of the upper genital tract by vaginal bacterial species in nonpregnant women.
      but the decidua is thought to be sterile during pregnancy.
      Figure thumbnail gr7
      Figure 7Stages of ascending intraamniotic infection
      Modified from Figure 1 in Romero R.
      • Romero R.
      • Mazor M.
      Infection and preterm labor.
      Stage I in the process of ascending infection corresponds to a change in the vaginal/cervical microbial flora or the presence of pathologic organisms in the cervix. Once microorganisms gain access to the amniotic cavity, they reside in the lower pole of the uterus between the membranes and the chorion (stage II). The microorganisms proceed through the amnion into the amniotic cavity that leads to an intraamniotic infection (stage III). The microorganisms may invade the fetus by different ports of entry (stage IV).
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.
      Figure thumbnail gr8
      Figure 8Progression of intraamniotic infection
      Modified from Figure 5 in Kim MJ, et al.
      • Kim M.J.
      • Romero R.
      • Gervasi M.T.
      • et al.
      Widespread microbial invasion of the chorioamniotic membranes is a consequence and not a cause of intra-amniotic infection.
      A, Most cases of microbial invasion of the amniotic cavity are the result of ascending infection from the vagina and cervix. B, Extensive microbial invasion of the amniotic cavity can result in fetal infection (bacteria are located in the fetal lung) and damaged chorioamniotic membranes (ie, necrotizing chorioamnionitis). The destruction of the amnion epithelium is a cardinal feature of necrotizing chorioamnionitis.
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.
      A hematogenous pathway can operate during the course of blood-borne maternal infections.
      • Cunningham F.G.
      • Morris G.B.
      • Mickal A.
      Acute pyelonephritis of pregnancy: a clinical review.
      • Benedetti T.J.
      • Valle R.
      • Ledger W.J.
      Antepartum pneumonia in pregnancy.
      • Kaul A.K.
      • Khan S.
      • Martens M.G.
      • Crosson J.T.
      • Lupo V.R.
      • Kaul R.
      Experimental gestational pyelonephritis induces preterm births and low birth weights in C3H/HeJ mice.
      Microorganisms such as Listeria monocytogenes,
      • Rivera-Alsina M.E.
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      • Kohl S.
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      Listeria monocytogenes: an important pathogen in premature labor and intrauterine fetal sepsis.
      • Romero R.
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      • Wan M.
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      Listeria monocytogenes chorioamnionitis and preterm labor.
      • Mazor M.
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      Listeria monocytogenes: the role of transabdominal amniocentesis in febrile patients with preterm labor.
       Treponema pallidum, Yersinia pestis, cytomegalovirus, Plasmodium species, and others can gain access through the maternal circulation to the intervillous space, from where they invade the villi and the fetal circulation.
      • Romero R.
      • Mazor M.
      Infection and preterm labor.
      Bacteria involved in periodontal disease may use this pathway to reach the amniotic cavity.
      • Offenbacher S.
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      Maternal periodontitis and prematurity: part I, obstetric outcome of prematurity and growth restriction.
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      Possible association between amniotic fluid micro-organism infection and microflora in the mouth.
      • Offenbacher S.
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      • Beck J.
      • Offenbacher S.
      Fetal immune response to oral pathogens and risk of preterm birth.
      • Boggess K.A.
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      Chronic maternal and fetal Porphyromonas gingivalis exposure during pregnancy in rabbits.
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      • et al.
      The effects of intra-amniotic injection of periodontopathic lipopolysaccharides in sheep.
      • Leon R.
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      • et al.
      Detection of Porphyromonas gingivalis in the amniotic fluid in pregnant women with a diagnosis of threatened premature labor.
      Intraamniotic infection has been documented in patients with preterm labor with intact membranes,
      • Romero R.
      • Miranda J.
      • Chaiworapongsa T.
      • et al.
      A novel molecular microbiologic technique for the rapid diagnosis of microbial invasion of the amniotic cavity and intra-amniotic infection in preterm labor with intact membranes.
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      • Gravett M.G.
      • Hummel D.
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      • Holmes K.K.
      Preterm labor associated with subclinical amniotic fluid infection and with bacterial vaginosis.
      • Leigh J.
      • Garite T.J.
      Amniocentesis and the management of premature labor.
      • Romero R.
      • Emamian M.
      • Quintero R.
      • et al.
      The value and limitations of the Gram stain examination in the diagnosis of intraamniotic infection.
      • Romero R.
      • Sirtori M.
      • Oyarzun E.
      • et al.
      Infection and labor: V, prevalence, microbiology, and clinical significance of intraamniotic infection in women with preterm labor and intact membranes.
      • Romero R.
      • Avila C.
      • Santhanam U.
      • Sehgal P.B.
      Amniotic fluid interleukin 6 in preterm labor: association with infection.
      • Romero R.
      • Jimenez C.
      • Lohda A.K.
      • et al.
      Amniotic fluid glucose concentration: a rapid and simple method for the detection of intraamniotic infection in preterm labor.
      • Romero R.
      • Quintero R.
      • Nores J.
      • et al.
      Amniotic fluid white blood cell count: a rapid and simple test to diagnose microbial invasion of the amniotic cavity and predict preterm delivery.
      • Gauthier D.W.
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      Correlation of amniotic fluid glucose concentration and intraamniotic infection in patients with preterm labor or premature rupture of membranes.
      • Coultrip L.L.
      • Grossman J.H.
      Evaluation of rapid diagnostic tests in the detection of microbial invasion of the amniotic cavity.
      • Watts D.H.
      • Krohn M.A.
      • Hillier S.L.
      • Eschenbach D.A.
      The association of occult amniotic fluid infection with gestational age and neonatal outcome among women in preterm labor.
      • Romero R.
      • Yoon B.H.
      • Mazor M.
      • et al.
      The diagnostic and prognostic value of amniotic fluid white blood cell count, glucose, interleukin-6, and Gram stain in patients with preterm labor and intact membranes.
      • Coultrip L.L.
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      The value of amniotic fluid interleukin-6 determination in patients with preterm labor and intact membranes in the detection of microbial invasion of the amniotic cavity.
      • Yoon B.H.
      • Yang S.H.
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      • Park K.H.
      • Kim C.J.
      • Romero R.
      Maternal blood C-reactive protein, white blood cell count, and temperature in preterm labor: a comparison with amniotic fluid white blood cell count.
      • Yoon B.H.
      • Chang J.W.
      • Romero R.
      Isolation of Ureaplasma urealyticum from the amniotic cavity and adverse outcome in preterm labor.
      • Greci L.S.
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      • Izquierdo L.A.
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      • Curet L.B.
      Is amniotic fluid analysis the key to preterm labor? A model using interleukin-6 for predicting rapid delivery.
      • Oyarzun E.
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      Antibiotic treatment in preterm labor and intact membranes: a randomized, double-blinded, placebo-controlled trial.
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      • Locksmith G.J.
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      Amniotic fluid matrix metalloproteinase-9 levels in women with preterm labor and suspected intra-amniotic infection.
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      • Gomez R.
      • et al.
      [Premature labor with intact membranes: microbiology of the amniotic fluid and lower genital tract and its relation with maternal and neonatal outcome].
      • Yoon B.H.
      • Romero R.
      • Moon J.B.
      • et al.
      Clinical significance of intra-amniotic inflammation in patients with preterm labor and intact membranes.
      • Digiulio D.B.
      • Romero R.
      • Amogan H.P.
      • et al.
      Microbial prevalence, diversity and abundance in amniotic fluid during preterm labor: a molecular and culture-based investigation.
      • Romero R.
      • Kadar N.
      • Miranda J.
      • et al.
      The diagnostic performance of the Mass Restricted (MR) score in the identification of microbial invasion of the amniotic cavity or intra-amniotic inflammation is not superior to amniotic fluid interleukin-6.
      • Combs C.A.
      • Gravett M.
      • Garite T.J.
      • et al.
      Amniotic fluid infection, inflammation, and colonization in preterm labor with intact membranes.
      • Chaemsaithong P.
      • Romero R.
      • Korzeniewski S.J.
      • et al.
      A rapid interleukin-6 bedside test for the identification of intra-amniotic inflammation in preterm labor with intact membranes.
      • Combs C.A.
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      Detection of microbial invasion of the amniotic cavity by analysis of cervicovaginal proteins in women with preterm labor and intact membranes.
      preterm prelabor rupture of the membranes,
      • Romero R.
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      • Chaemsaithong P.
      • et al.
      Sterile and microbial-associated intra-amniotic inflammation in preterm prelabor rupture of membranes.
      • Garite T.J.
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      • Garite T.J.
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      • Cotton D.B.
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      • Zlatnik F.J.
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      Amniocentesis for gram stain and culture in preterm premature rupture of the membranes.
      • Feinstein S.J.
      • Vintzileos A.M.
      • Lodeiro J.G.
      • Campbell W.A.
      • Weinbaum P.J.
      • Nochimson D.J.
      Amniocentesis with premature rupture of membranes.
      • Vintzileos A.M.
      • Campbell W.A.
      • Nochimson D.J.
      • Weinbaum P.J.
      • Escoto D.T.
      • Mirochnick M.H.
      Qualitative amniotic fluid volume versus amniocentesis in predicting infection in preterm premature rupture of the membranes.
      • Romero R.
      • Quintero R.
      • Oyarzun E.
      • et al.
      Intraamniotic infection and the onset of labor in preterm premature rupture of the membranes.
      • Gauthier D.W.
      • Meyer W.J.
      Comparison of gram stain, leukocyte esterase activity, and amniotic fluid glucose concentration in predicting amniotic fluid culture results in preterm premature rupture of membranes.
      • Romero R.
      • Yoon B.H.
      • Mazor M.
      • et al.
      A comparative study of the diagnostic performance of amniotic fluid glucose, white blood cell count, interleukin-6, and gram stain in the detection of microbial invasion in patients with preterm premature rupture of membranes.
      • Averbuch B.
      • Mazor M.
      • Shoham-Vardi I.
      • et al.
      Intra-uterine infection in women with preterm premature rupture of membranes: maternal and neonatal characteristics.
      • Carroll S.G.
      • Papaioannou S.
      • Ntumazah I.L.
      • Philpott-Howard J.
      • Nicolaides K.H.
      Lower genital tract swabs in the prediction of intrauterine infection in preterm prelabour rupture of the membranes.
      • Digiulio D.B.
      • Romero R.
      • Kusanovic J.P.
      • et al.
      Prevalence and diversity of microbes in the amniotic fluid, the fetal inflammatory response, and pregnancy outcome in women with preterm pre-labor rupture of membranes.
      • Kacerovsky M.
      • Musilova I.
      • Khatibi A.
      • et al.
      Intraamniotic inflammatory response to bacteria: analysis of multiple amniotic fluid proteins in women with preterm prelabor rupture of membranes.
      • Kacerovsky M.
      • Musilova I.
      • Andrys C.
      • et al.
      Prelabor rupture of membranes between 34 and 37 weeks: the intraamniotic inflammatory response and neonatal outcomes.
      • Chaemsaithong P.
      • Romero R.
      • Korzeniewski S.J.
      • et al.
      A point of care test for interleukin-6 in amniotic fluid in preterm prelabor rupture of membranes: a step toward the early treatment of acute intra-amniotic inflammation/infection.
      cervical insufficiency,
      • Romero R.
      • Gonzalez R.
      • Sepulveda W.
      • et al.
      Infection and labor: VIII, microbial invasion of the amniotic cavity in patients with suspected cervical incompetence: prevalence and clinical significance.
      • Mays J.K.
      • Figueroa R.
      • Shah J.
      • Khakoo H.
      • Kaminsky S.
      • Tejani N.
      Amniocentesis for selection before rescue cerclage.
      • Lee S.E.
      • Romero R.
      • Park C.W.
      • Jun J.K.
      • Yoon B.H.
      The frequency and significance of intraamniotic inflammation in patients with cervical insufficiency.
      • Bujold E.
      • Morency A.M.
      • Rallu F.
      • et al.
      Bacteriology of amniotic fluid in women with suspected cervical insufficiency.
      • Oh K.J.
      • Lee S.E.
      • Jung H.
      • Kim G.
      • Romero R.
      • Yoon B.H.
      Detection of ureaplasmas by the polymerase chain reaction in the amniotic fluid of patients with cervical insufficiency.
      asymptomatic short cervix,
      • Romero R.
      • Miranda J.
      • Chaiworapongsa T.
      • et al.
      Sterile intra-amniotic inflammation in asymptomatic patients with a sonographic short cervix: prevalence and clinical significance.
      • Gomez R.
      • Romero R.
      • Nien J.K.
      • et al.
      A short cervix in women with preterm labor and intact membranes: a risk factor for microbial invasion of the amniotic cavity.
      • Hassan S.
      • Romero R.
      • Hendler I.
      • et al.
      A sonographic short cervix as the only clinical manifestation of intra-amniotic infection.
      • Vaisbuch E.
      • Hassan S.S.
      • Mazaki-Tovi S.
      • et al.
      Patients with an asymptomatic short cervix (≤15 mm) have a high rate of subclinical intraamniotic inflammation: implications for patient counseling.
      idiopathic vaginal bleeding,
      • Gomez R.
      • Romero R.
      • Nien J.K.
      • et al.
      Idiopathic vaginal bleeding during pregnancy as the only clinical manifestation of intrauterine infection.
      placenta previa,
      • Madan I.
      • Romero R.
      • Kusanovic J.P.
      • et al.
      The frequency and clinical significance of intra-amniotic infection and/or inflammation in women with placenta previa and vaginal bleeding: an unexpected observation.
      and clinical chorioamnionitis at term.
      • Romero R.
      • Miranda J.
      • Kusanovic J.P.
      • et al.
      Clinical chorioamnionitis at term I: microbiology of the amniotic cavity using cultivation and molecular techniques.
      Rupture of the membranes is not necessary for bacteria to reach the amniotic cavity; indeed, there is experimental evidence that bacteria can cross intact membranes.
      • Galask R.P.
      • Varner M.W.
      • Petzold C.R.
      • Wilbur S.L.
      Bacterial attachment to the chorioamniotic membranes.
      Most of these infections are subclinical in nature; therefore, they occur in the absence of clinical chorioamnionitis.
      • Gravett M.G.
      • Hummel D.
      • Eschenbach D.A.
      • Holmes K.K.
      Preterm labor associated with subclinical amniotic fluid infection and with bacterial vaginosis.
      • Romero R.
      • Gomez R.
      • Chaiworapongsa T.
      • Conoscenti G.
      • Kim J.C.
      • Kim Y.M.
      The role of infection in preterm labour and delivery.
      • Romero R.
      • Espinoza J.
      • Goncalves L.F.
      • Kusanovic J.P.
      • Friel L.
      • Hassan S.
      The role of inflammation and infection in preterm birth.
      Hence, these infections are undetected unless the amniotic fluid is analyzed. The most frequent microorganisms found in the amniotic cavity are genital mycoplasmas,
      • Romero R.
      • Sirtori M.
      • Oyarzun E.
      • et al.
      Infection and labor: V, prevalence, microbiology, and clinical significance of intraamniotic infection in women with preterm labor and intact membranes.
      • Yoon B.H.
      • Chang J.W.
      • Romero R.
      Isolation of Ureaplasma urealyticum from the amniotic cavity and adverse outcome in preterm labor.
      • Romero R.
      • Quintero R.
      • Oyarzun E.
      • et al.
      Intraamniotic infection and the onset of labor in preterm premature rupture of the membranes.
      • Romero R.
      • Gomez R.
      • Chaiworapongsa T.
      • Conoscenti G.
      • Kim J.C.
      • Kim Y.M.
      The role of infection in preterm labour and delivery.
      • Romero R.
      • Garite T.J.
      Twenty percent of very preterm neonates (23-32 weeks of gestation) are born with bacteremia caused by genital Mycoplasmas.
      • Oh K.J.
      • Lee K.A.
      • Sohn Y.K.
      • et al.
      Intraamniotic infection with genital mycoplasmas exhibits a more intense inflammatory response than intraamniotic infection with other microorganisms in patients with preterm premature rupture of membranes.
      • Digiulio D.B.
      Diversity of microbes in amniotic fluid.
      • Allen-Daniels M.J.
      • Serrano M.G.
      • Pflugner L.P.
      • et al.
      Identification of a gene in Mycoplasma hominis associated with preterm birth and microbial burden in intraamniotic infection.
      in particular, Ureaplasma species,
      • Oh K.J.
      • Lee S.E.
      • Jung H.
      • Kim G.
      • Romero R.
      • Yoon B.H.
      Detection of ureaplasmas by the polymerase chain reaction in the amniotic fluid of patients with cervical insufficiency.
      • Gravett M.G.
      • Eschenbach D.A.
      Possible role of Ureaplasma urealyticum in preterm premature rupture of the fetal membranes.
      • Yoon B.H.
      • Romero R.
      • Park J.S.
      • et al.
      Microbial invasion of the amniotic cavity with Ureaplasma urealyticum is associated with a robust host response in fetal, amniotic, and maternal compartments.
      • Yoon B.H.
      • Romero R.
      • Kim M.
      • et al.
      Clinical implications of detection of Ureaplasma urealyticum in the amniotic cavity with the polymerase chain reaction.
      • Yoon B.H.
      • Romero R.
      • Lim J.H.
      • et al.
      The clinical significance of detecting Ureaplasma urealyticum by the polymerase chain reaction in the amniotic fluid of patients with preterm labor.
      • Kim M.
      • Kim G.
      • Romero R.
      • Shim S.S.
      • Kim E.C.
      • Yoon B.H.
      Biovar diversity of Ureaplasma urealyticum in amniotic fluid: distribution, intrauterine inflammatory response and pregnancy outcomes.
      • Gerber S.
      • Vial Y.
      • Hohlfeld P.
      • Witkin S.S.
      Detection of Ureaplasma urealyticum in second-trimester amniotic fluid by polymerase chain reaction correlates with subsequent preterm labor and delivery.
      • Perni S.C.
      • Vardhana S.
      • Korneeva I.
      • et al.
      Mycoplasma hominis and Ureaplasma urealyticum in midtrimester amniotic fluid: association with amniotic fluid cytokine levels and pregnancy outcome.
      • Jacobsson B.
      • Aaltonen R.
      • Rantakokko-Jalava K.
      • Morken N.H.
      • Alanen A.
      Quantification of Ureaplasma urealyticum DNA in the amniotic fluid from patients in PTL and pPROM and its relation to inflammatory cytokine levels.
       Gardnerella vaginalis,
      • Romero R.
      • Miranda J.
      • Kusanovic J.P.
      • et al.
      Clinical chorioamnionitis at term I: microbiology of the amniotic cavity using cultivation and molecular techniques.
      • Gravett M.G.
      • Hummel D.
      • Eschenbach D.A.
      • Holmes K.K.
      Preterm labor associated with subclinical amniotic fluid infection and with bacterial vaginosis.
      • Digiulio D.B.
      • Romero R.
      • Kusanovic J.P.
      • et al.
      Prevalence and diversity of microbes in the amniotic fluid, the fetal inflammatory response, and pregnancy outcome in women with preterm pre-labor rupture of membranes.
      • Lewis J.F.
      • Johnson P.
      • Miller P.
      Evaluation of amniotic fluid for aerobic and anaerobic bacteria.
      • Martius J.
      • Eschenbach D.A.
      The role of bacterial vaginosis as a cause of amniotic fluid infection, chorioamnionitis and prematurity: a review.
      • Hillier S.L.
      • Krohn M.A.
      • Cassen E.
      • Easterling T.R.
      • Rabe L.K.
      • Eschenbach D.A.
      The role of bacterial vaginosis and vaginal bacteria in amniotic fluid infection in women in preterm labor with intact fetal membranes.
      , and Fusobacteria species.
      • Romero R.
      • Miranda J.
      • Chaiworapongsa T.
      • et al.
      A novel molecular microbiologic technique for the rapid diagnosis of microbial invasion of the amniotic cavity and intra-amniotic infection in preterm labor with intact membranes.
      • Digiulio D.B.
      • Romero R.
      • Amogan H.P.
      • et al.
      Microbial prevalence, diversity and abundance in amniotic fluid during preterm labor: a molecular and culture-based investigation.
      • Digiulio D.B.
      • Romero R.
      • Kusanovic J.P.
      • et al.
      Prevalence and diversity of microbes in the amniotic fluid, the fetal inflammatory response, and pregnancy outcome in women with preterm pre-labor rupture of membranes.
      Fungi can also be found; women who become pregnant while using intrauterine contraceptive devices are at high risk for intraamniotic infection with Candida albicans.
      • Romero R.
      • Reece E.A.
      • Duff G.W.
      • Coultrip L.
      • Hobbins J.C.
      Prenatal diagnosis of Candida albicans chorioamnionitis.
      • Bruner J.P.
      • Elliott J.P.
      • Kilbride H.W.
      • Garite T.J.
      • Knox G.E.
      Candida chorioamnionitis diagnosed by amniocentesis with subsequent fetal infection.
      • Smith C.V.
      • Horenstein J.
      • Platt L.D.
      Intraamniotic infection with Candida albicans associated with a retained intrauterine contraceptive device: a case report.
      • Chaim W.
      • Mazor M.
      • Wiznitzer A.
      The prevalence and clinical significance of intraamniotic infection with Candida species in women with preterm labor.
      • Chaim W.
      • Mazor M.
      Pregnancy with an intrauterine device in situ and preterm delivery.
      • Berry D.L.
      • Olson G.L.
      • Wen T.S.
      • Belfort M.A.
      • Moise Jr., K.J.
      Candida chorioamnionitis: a report of two cases.
      • Qureshi F.
      • Jacques S.M.
      • Bendon R.W.
      • et al.
      Candida funisitis: a clinicopathologic study of 32 cases.
      • Barth T.
      • Broscheit J.
      • Bussen S.
      • Dietl J.
      Maternal sepsis and intrauterine fetal death resulting from Candida tropicalis chorioamnionitis in a woman with a retained intrauterine contraceptive device.
      • Crawford J.T.
      • Pereira L.
      • Buckmaster J.
      • Gravett M.G.
      • Tolosa J.E.
      Amniocentesis results and novel proteomic analysis in a case of occult candidal chorioamnionitis.
      • Kim S.K.
      • Romero R.
      • Kusanovic J.P.
      • et al.
      The prognosis of pregnancy conceived despite the presence of an intrauterine device (IUD).
      Polymicrobial invasion of the amniotic cavity is present in approximately 30% of cases.
      • Romero R.
      • Miranda J.
      • Chaiworapongsa T.
      • et al.
      A novel molecular microbiologic technique for the rapid diagnosis of microbial invasion of the amniotic cavity and intra-amniotic infection in preterm labor with intact membranes.
      • Romero R.
      • Miranda J.
      • Chaemsaithong P.
      • et al.
      Sterile and microbial-associated intra-amniotic inflammation in preterm prelabor rupture of membranes.
      • Romero R.
      • Sirtori M.
      • Oyarzun E.
      • et al.
      Infection and labor: V, prevalence, microbiology, and clinical significance of intraamniotic infection in women with preterm labor and intact membranes.
      • Digiulio D.B.
      • Romero R.
      • Amogan H.P.
      • et al.
      Microbial prevalence, diversity and abundance in amniotic fluid during preterm labor: a molecular and culture-based investigation.
      • Digiulio D.B.
      • Romero R.
      • Kusanovic J.P.
      • et al.
      Prevalence and diversity of microbes in the amniotic fluid, the fetal inflammatory response, and pregnancy outcome in women with preterm pre-labor rupture of membranes.
      • Jalava J.
      • Mantymaa M.L.
      • Ekblad U.
      • et al.
      Bacterial 16S rDNA polymerase chain reaction in the detection of intra-amniotic infection.
       Table 2 contains information about the frequency of microbial invasion of the amniotic cavity in different obstetrical syndromes. Table 3 lists the microorganisms detected in the amniotic cavity of patients with preterm labor with intact membranes
      • Digiulio D.B.
      • Romero R.
      • Amogan H.P.
      • et al.
      Microbial prevalence, diversity and abundance in amniotic fluid during preterm labor: a molecular and culture-based investigation.
      and clinical chorioamnionitis at term.
      • Romero R.
      • Miranda J.
      • Kusanovic J.P.
      • et al.
      Clinical chorioamnionitis at term I: microbiology of the amniotic cavity using cultivation and molecular techniques.
      Table 2The frequency of microbial invasion of the amniotic cavity in obstetrical disorders
      As determined by amniotic fluid studies that were obtained by transabdominal amniocentesis with the use of cultivation techniques.
      Obstetrical disordersPrevalence of microbial invasion of the amniotic cavity (%)
      Spontaneous labor at term with intact membranes6.3-18.8
      • Seong H.S.
      • Lee S.E.
      • Kang J.H.
      • Romero R.
      • Yoon B.H.
      The frequency of microbial invasion of the amniotic cavity and histologic chorioamnionitis in women at term with intact membranes in the presence or absence of labor.
      • Romero R.
      • Nores J.
      • Mazor M.
      • et al.
      Microbial invasion of the amniotic cavity during term labor: prevalence and clinical significance.
      • Gomez R.
      • Romero R.
      • Galasso M.
      • Behnke E.
      • Insunza A.
      • Cotton D.B.
      The value of amniotic fluid interleukin-6, white blood cell count, and gram stain in the diagnosis of microbial invasion of the amniotic cavity in patients at term.
      • Yoon B.H.
      • Romero R.
      • Moon J.
      • et al.
      Differences in the fetal interleukin-6 response to microbial invasion of the amniotic cavity between term and preterm gestation.
      Preterm labor with intact membranes8.7-34
      • Romero R.
      • Miranda J.
      • Chaiworapongsa T.
      • et al.
      A novel molecular microbiologic technique for the rapid diagnosis of microbial invasion of the amniotic cavity and intra-amniotic infection in preterm labor with intact membranes.
      • Hameed C.
      • Tejani N.
      • Verma U.L.
      • Archbald F.
      Silent chorioamnionitis as a cause of preterm labor refractory to tocolytic therapy.
      • Gravett M.G.
      • Hummel D.
      • Eschenbach D.A.
      • Holmes K.K.
      Preterm labor associated with subclinical amniotic fluid infection and with bacterial vaginosis.
      • Leigh J.
      • Garite T.J.
      Amniocentesis and the management of premature labor.
      • Romero R.
      • Emamian M.
      • Quintero R.
      • et al.
      The value and limitations of the Gram stain examination in the diagnosis of intraamniotic infection.
      • Romero R.
      • Sirtori M.
      • Oyarzun E.
      • et al.
      Infection and labor: V, prevalence, microbiology, and clinical significance of intraamniotic infection in women with preterm labor and intact membranes.
      • Romero R.
      • Avila C.
      • Santhanam U.
      • Sehgal P.B.
      Amniotic fluid interleukin 6 in preterm labor: association with infection.
      • Romero R.
      • Jimenez C.
      • Lohda A.K.
      • et al.
      Amniotic fluid glucose concentration: a rapid and simple method for the detection of intraamniotic infection in preterm labor.
      • Romero R.
      • Quintero R.
      • Nores J.
      • et al.
      Amniotic fluid white blood cell count: a rapid and simple test to diagnose microbial invasion of the amniotic cavity and predict preterm delivery.
      • Gauthier D.W.
      • Meyer W.J.
      • Bieniarz A.
      Correlation of amniotic fluid glucose concentration and intraamniotic infection in patients with preterm labor or premature rupture of membranes.
      • Coultrip L.L.
      • Grossman J.H.
      Evaluation of rapid diagnostic tests in the detection of microbial invasion of the amniotic cavity.
      • Watts D.H.
      • Krohn M.A.
      • Hillier S.L.
      • Eschenbach D.A.
      The association of occult amniotic fluid infection with gestational age and neonatal outcome among women in preterm labor.
      • Romero R.
      • Yoon B.H.
      • Mazor M.
      • et al.
      The diagnostic and prognostic value of amniotic fluid white blood cell count, glucose, interleukin-6, and Gram stain in patients with preterm labor and intact membranes.
      • Coultrip L.L.
      • Lien J.M.
      • Gomez R.
      • Kapernick P.
      • Khoury A.
      • Grossman J.H.
      The value of amniotic fluid interleukin-6 determination in patients with preterm labor and intact membranes in the detection of microbial invasion of the amniotic cavity.
      • Yoon B.H.
      • Yang S.H.
      • Jun J.K.
      • Park K.H.
      • Kim C.J.
      • Romero R.
      Maternal blood C-reactive protein, white blood cell count, and temperature in preterm labor: a comparison with amniotic fluid white blood cell count.
      • Yoon B.H.
      • Chang J.W.
      • Romero R.
      Isolation of Ureaplasma urealyticum from the amniotic cavity and adverse outcome in preterm labor.
      • Greci L.S.
      • Gilson G.J.
      • Nevils B.
      • Izquierdo L.A.
      • Qualls C.R.
      • Curet L.B.
      Is amniotic fluid analysis the key to preterm labor? A model using interleukin-6 for predicting rapid delivery.
      • Gonzalez-Bosquet E.
      • Cerqueira M.J.
      • Dominguez C.
      • Gasser I.
      • Bermejo B.
      • Cabero L.
      Amniotic fluid glucose and cytokines values in the early diagnosis of amniotic infection in patients with preterm labor and intact membranes.
      • Locksmith G.J.
      • Clark P.
      • Duff P.
      • Schultz G.S.
      Amniotic fluid matrix metalloproteinase-9 levels in women with preterm labor and suspected intra-amniotic infection.
      • Ovalle A.
      • Martinez M.A.
      • Gomez R.
      • et al.
      [Premature labor with intact membranes: microbiology of the amniotic fluid and lower genital tract and its relation with maternal and neonatal outcome].
      • Yoon B.H.
      • Romero R.
      • Moon J.B.
      • et al.
      Clinical significance of intra-amniotic inflammation in patients with preterm labor and intact membranes.
      • Digiulio D.B.
      • Romero R.
      • Amogan H.P.
      • et al.
      Microbial prevalence, diversity and abundance in amniotic fluid during preterm labor: a molecular and culture-based investigation.
      • Romero R.
      • Kadar N.
      • Miranda J.
      • et al.
      The diagnostic performance of the Mass Restricted (MR) score in the identification of microbial invasion of the amniotic cavity or intra-amniotic inflammation is not superior to amniotic fluid interleukin-6.
      • Combs C.A.
      • Gravett M.
      • Garite T.J.
      • et al.
      Amniotic fluid infection, inflammation, and colonization in preterm labor with intact membranes.
      • Chaemsaithong P.
      • Romero R.
      • Korzeniewski S.J.
      • et al.
      A rapid interleukin-6 bedside test for the identification of intra-amniotic inflammation in preterm labor with intact membranes.
      • Combs C.A.
      • Garite T.J.
      • Lapidus J.A.
      • et al.
      Detection of microbial invasion of the amniotic cavity by analysis of cervicovaginal proteins in women with preterm labor and intact membranes.
      • Gomez R.
      • Romero R.
      • Ghezzi F.
      • Yoon B.H.
      • Mazor M.
      • Berry S.M.
      The fetal inflammatory response syndrome.
      Preterm prelabor rupture of the membranes without labor17-57.7
      • Romero R.
      • Miranda J.
      • Chaemsaithong P.
      • et al.
      Sterile and microbial-associated intra-amniotic inflammation in preterm prelabor rupture of membranes.
      • Gauthier D.W.
      • Meyer W.J.
      • Bieniarz A.
      Correlation of amniotic fluid glucose concentration and intraamniotic infection in patients with preterm labor or premature rupture of membranes.
      • Coultrip L.L.
      • Grossman J.H.
      Evaluation of rapid diagnostic tests in the detection of microbial invasion of the amniotic cavity.
      • Garite T.J.
      • Freeman R.K.
      • Linzey E.M.
      • Braly P.
      The use of amniocentesis in patients with premature rupture of membranes.
      • Garite T.J.
      • Freeman R.K.
      Chorioamnionitis in the preterm gestation.
      • Cotton D.B.
      • Hill L.M.
      • Strassner H.T.
      • Platt L.D.
      • Ledger W.J.
      Use of amniocentesis in preterm gestation with ruptured membranes.
      • Zlatnik F.J.
      • Cruikshank D.P.
      • Petzold C.R.
      • Galask R.P.
      Amniocentesis in the identification of inapparent infection in preterm patients with premature rupture of the membranes.
      • Broekhuizen F.F.
      • Gilman M.
      • Hamilton P.R.
      Amniocentesis for gram stain and culture in preterm premature rupture of the membranes.
      • Feinstein S.J.
      • Vintzileos A.M.
      • Lodeiro J.G.
      • Campbell W.A.
      • Weinbaum P.J.
      • Nochimson D.J.
      Amniocentesis with premature rupture of membranes.
      • Vintzileos A.M.
      • Campbell W.A.
      • Nochimson D.J.
      • Weinbaum P.J.
      • Escoto D.T.
      • Mirochnick M.H.
      Qualitative amniotic fluid volume versus amniocentesis in predicting infection in preterm premature rupture of the membranes.
      • Romero R.
      • Quintero R.
      • Oyarzun E.
      • et al.
      Intraamniotic infection and the onset of labor in preterm premature rupture of the membranes.
      • Gauthier D.W.
      • Meyer W.J.
      Comparison of gram stain, leukocyte esterase activity, and amniotic fluid glucose concentration in predicting amniotic fluid culture results in preterm premature rupture of membranes.
      • Romero R.
      • Yoon B.H.
      • Mazor M.
      • et al.
      A comparative study of the diagnostic performance of amniotic fluid glucose, white blood cell count, interleukin-6, and gram stain in the detection of microbial invasion in patients with preterm premature rupture of membranes.
      • Averbuch B.
      • Mazor M.
      • Shoham-Vardi I.
      • et al.
      Intra-uterine infection in women with preterm premature rupture of membranes: maternal and neonatal characteristics.
      • Carroll S.G.
      • Papaioannou S.
      • Ntumazah I.L.
      • Philpott-Howard J.
      • Nicolaides K.H.
      Lower genital tract swabs in the prediction of intrauterine infection in preterm prelabour rupture of the membranes.
      • Digiulio D.B.
      • Romero R.
      • Kusanovic J.P.
      • et al.
      Prevalence and diversity of microbes in the amniotic fluid, the fetal inflammatory response, and pregnancy outcome in women with preterm pre-labor rupture of membranes.
      • Kacerovsky M.
      • Musilova I.
      • Khatibi A.
      • et al.
      Intraamniotic inflammatory response to bacteria: analysis of multiple amniotic fluid proteins in women with preterm prelabor rupture of membranes.
      • Kacerovsky M.
      • Musilova I.
      • Andrys C.
      • et al.
      Prelabor rupture of membranes between 34 and 37 weeks: the intraamniotic inflammatory response and neonatal outcomes.
      • Chaemsaithong P.
      • Romero R.
      • Korzeniewski S.J.
      • et al.
      A point of care test for interleukin-6 in amniotic fluid in preterm prelabor rupture of membranes: a step toward the early treatment of acute intra-amniotic inflammation/infection.
      • Gomez R.
      • Romero R.
      • Ghezzi F.
      • Yoon B.H.
      • Mazor M.
      • Berry S.M.
      The fetal inflammatory response syndrome.
      Clinical chorioamnionitis at term61
      • Romero R.
      • Miranda J.
      • Kusanovic J.P.
      • et al.
      Clinical chorioamnionitis at term I: microbiology of the amniotic cavity using cultivation and molecular techniques.
      Preterm prelabor rupture of the membranes in labor75
      • Romero R.
      • Quintero R.
      • Oyarzun E.
      • et al.
      Intraamniotic infection and the onset of labor in preterm premature rupture of the membranes.
      Spontaneous rupture of membranes at term34.3
      • Romero R.
      • Mazor M.
      • Morrotti R.
      • et al.
      Infection and labor. VII, Microbial invasion of the amniotic cavity in spontaneous rupture of membranes at term.
      Sonographic short cervix2.2-9
      • Romero R.
      • Miranda J.
      • Chaiworapongsa T.
      • et al.
      Sterile intra-amniotic inflammation in asymptomatic patients with a sonographic short cervix: prevalence and clinical significance.
      • Gomez R.
      • Romero R.
      • Nien J.K.
      • et al.
      A short cervix in women with preterm labor and intact membranes: a risk factor for microbial invasion of the amniotic cavity.
      • Hassan S.
      • Romero R.
      • Hendler I.
      • et al.
      A sonographic short cervix as the only clinical manifestation of intra-amniotic infection.
      • Vaisbuch E.
      • Hassan S.S.
      • Mazaki-Tovi S.
      • et al.
      Patients with an asymptomatic short cervix (≤15 mm) have a high rate of subclinical intraamniotic inflammation: implications for patient counseling.
      Cervical insufficiency8-51.5
      • Romero R.
      • Gonzalez R.
      • Sepulveda W.
      • et al.
      Infection and labor: VIII, microbial invasion of the amniotic cavity in patients with suspected cervical incompetence: prevalence and clinical significance.
      • Mays J.K.
      • Figueroa R.
      • Shah J.
      • Khakoo H.
      • Kaminsky S.
      • Tejani N.
      Amniocentesis for selection before rescue cerclage.
      • Lee S.E.
      • Romero R.
      • Park C.W.
      • Jun J.K.
      • Yoon B.H.
      The frequency and significance of intraamniotic inflammation in patients with cervical insufficiency.
      • Bujold E.
      • Morency A.M.
      • Rallu F.
      • et al.
      Bacteriology of amniotic fluid in women with suspected cervical insufficiency.
      • Oh K.J.
      • Lee S.E.
      • Jung H.
      • Kim G.
      • Romero R.
      • Yoon B.H.
      Detection of ureaplasmas by the polymerase chain reaction in the amniotic fluid of patients with cervical insufficiency.
      Twin gestations with preterm labor and intact membranes11.9-35
      • Romero R.
      • Shamma F.
      • Avila C.
      • et al.
      Infection and labor: VI, prevalence, microbiology, and clinical significance of intraamniotic infection in twin gestations with preterm labor.
      • Mazor M.
      • Hershkovitz R.
      • Ghezzi F.
      • Maymon E.
      • Horowitz S.
      • Leiberman J.R.
      Intraamniotic infection in patients with preterm labor and twin pregnancies.
      • Yoon B.H.
      • Park K.H.
      • Koo J.N.
      • et al.
      Intraamniotic infection of twin pregnancies with preterm labor.
      Meconium-stained amniotic fluid in preterm gestations33
      • Romero R.
      • Hanaoka S.
      • Mazor M.
      • et al.
      Meconium-stained amniotic fluid: a risk factor for microbial invasion of the amniotic cavity.
      Meconium-stained amniotic fluid in term gestations19.6
      • Romero R.
      • Yoon B.H.
      • Chaemsaithong P.
      • et al.
      Bacteria and endotoxin in meconium-stained amniotic fluid at term: could intra-amniotic infection cause meconium passage?.
      Placenta previa5.7
      • Madan I.
      • Romero R.
      • Kusanovic J.P.
      • et al.
      The frequency and clinical significance of intra-amniotic infection and/or inflammation in women with placenta previa and vaginal bleeding: an unexpected observation.
      Idiopathic vaginal bleeding14
      • Gomez R.
      • Romero R.
      • Nien J.K.
      • et al.
      Idiopathic vaginal bleeding during pregnancy as the only clinical manifestation of intrauterine infection.
      Pregnancy with intrauterine device45.9
      • Kim S.K.
      • Romero R.
      • Kusanovic J.P.
      • et al.
      The prognosis of pregnancy conceived despite the presence of an intrauterine device (IUD).
      Preeclampsia1.6
      • Digiulio D.B.
      • Gervasi M.
      • Romero R.
      • et al.
      Microbial invasion of the amniotic cavity in preeclampsia as assessed by cultivation and sequence-based methods.
      Small-for-gestational-age fetuses6
      • Digiulio D.B.
      • Gervasi M.T.
      • Romero R.
      • et al.
      Microbial invasion of the amniotic cavity in pregnancies with small-for-gestational-age fetuses.
      Stillbirth2.3-13.3
      • Blackwell S.
      • Romero R.
      • Chaiworapongsa T.
      • et al.
      Maternal and fetal inflammatory responses in unexplained fetal death.
      • Lannaman K.
      • Romero R.
      • Chaemsaithong P.
      • et al.
      Fetal death: an extreme form fo maternal anti-fetal rejection.
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.
      a As determined by amniotic fluid studies that were obtained by transabdominal amniocentesis with the use of cultivation techniques.
      Table 3Microorganisms in the amniotic cavity
      Detected with the use of cultivation and molecular microbiologic techniques in the amniotic fluid of patients with spontaneous preterm labor with intact membranes and patients with clinical chorioamnionitis at term.
      Patients with spontaneous preterm labor with intact membranes
      • Digiulio D.B.
      • Romero R.
      • Amogan H.P.
      • et al.
      Microbial prevalence, diversity and abundance in amniotic fluid during preterm labor: a molecular and culture-based investigation.
      Patients with clinical chorioamnionitis at term
      • Romero R.
      • Miranda J.
      • Kusanovic J.P.
      • et al.
      Clinical chorioamnionitis at term I: microbiology of the amniotic cavity using cultivation and molecular techniques.
      Fusobacterium nucleatumUreaplasma species
      Sneathia sanguinegensGardnerella vaginalis
      Ureaplasma speciesMycoplasma hominis
      Streptococcus mitisStreptococcus agalactiae
      Gardnerella vaginalisLactobacillus species
      Peptostreptococcus speciesBacteroides species
      Leptotrichia amnioniiAcinetobacter species
      Mycoplasma hominisSneathia
      Streptococcus agalactiaeStreptococcus viridans
      Lactobacillus speciesPorphyromonas species
      Bacillus speciesVeillonella species
      Coagulase-negative Staphylococcus speciesPeptostreptococcus species
      Prevotella speciesEscherichia coli
      Others: uncultivated Bacteroidetes, Delftia acidovorans, Neisseria cinereaPseudomonas aeruginosa
      Staphylococcus aureus
      Eubacterium species
      Gram negative bacilli
      Enterococcus species
      Others: Fusobacterium species, Candida species, Abiotrophia defective, Micrococcus luteus, Staphylococcus epidermidis, Firmicute, Propionibacterium acnes
      Kim. Acute inflammatory lesions of the placenta. Am J Obstet Gynecol 2015.
      a Detected with the use of cultivation and molecular microbiologic techniques in the amniotic fluid of patients with spontaneous preterm labor with intact membranes and patients with clinical chorioamnionitis at term.
      Microorganisms gaining access to the uterine cavity from the lower genital tract are first localized in the decidua of the supracervical region. Subsequent propagation and chorioamniotic passage of the microorganisms can lead to the establishment of microbial invasion of the amniotic cavity (Figures 7 and 8).
      • Goldenberg R.L.
      • Andrews W.W.
      • Hauth J.C.
      Choriodecidual infection and preterm birth.
      • Steel J.H.
      • Malatos S.
      • Kennea N.
      • et al.
      Bacteria and inflammatory cells in fetal membranes do not always cause preterm labor.
      Although some investigators believe that there is a stage in which the bacteria are located diffusely in the choriodecidual layer, our studies, using FISH with a bacterial 16S rRNA probe, indicate that there is not extensive involvement of the chorion-decidua in cases with microbial invasion of the amniotic cavity.
      • Kim M.J.
      • Romero R.
      • Gervasi M.T.
      • et al.
      Widespread microbial invasion of the chorioamniotic membranes is a consequence and not a cause of intra-amniotic infection.
      Indeed, bacteria are primarily found in the amnion in cases of intraamniotic infection, which indicates that microbial invasion of the amniotic cavity is a prerequisite for substantial invasion of the amnion and chorion.
      • Kim M.J.
      • Romero R.
      • Gervasi M.T.
      • et al.
      Widespread microbial invasion of the chorioamniotic membranes is a consequence and not a cause of intra-amniotic infection.
      Specifically, bacteria are detected more frequently in the amniotic fluid than in the chorioamniotic membranes of patients with positive amniotic fluid culture (100% vs 33%; P < .0001; Figure 9).
      • Kim M.J.
      • Romero R.
      • Gervasi M.T.
      • et al.
      Widespread microbial invasion of the chorioamniotic membranes is a consequence and not a cause of intra-amniotic infection.
      Figure thumbnail gr9
      Figure 9Bacterial invasion of amniotic epithelial cells demonstrated by fluorescent staining
      Modified from Figure 3C in Kim MJ, et al.
      • Kim M.J.
      • Romero R.
      • Gervasi M.T.
      • et al.
      Widespread microbial invasion of the chorioamniotic membranes is a consequence and not a cause of intra-amniotic infection.