The Alabama Preterm Birth Study: Umbilical cord blood Ureaplasma urealyticum and Mycoplasma hominis cultures in very preterm newborn infants

Materials and Methods 

The overall Alabama Preterm Birth Study, which included 457 consecutive singleton deliveries of infants born between 23-32 weeks from 1996-2001, has been described previously.12, 13, 14, 15, 16, 17 Findings from this data set related to IL-6 levels,12 inflammatory placental lesions,13 male/female differences in placental inflammatory markers,14 the use of corticosteroids in the face of placental inflammation,15 placental histolologic findings in recurrent preterm births,16 and the importance of the placental lesion—diffuse decidual leukocytoplastic necrosis17—have all been evaluated. The study reported here specifically focuses on the subset of 351 women/infant pairs in this population who had umbilical cord blood cultures for U urealyticum and M hominis.

A maternal chart review was performed by a trained research nurse to gather demographic and obstetric characteristics such as maternal race, education, age and parity, smoking status, diabetes and preeclampsia, and whether the delivery was spontaneous or indicated. The diagnosis of preclampsia required a blood pressure of greater than 140/90 mm Hg on at least 1 occasion and the presence of proteinuria (1+ or greater). Spontaneous preterm birth was defined as delivery after either spontaneous preterm labor or spontaneous PPROM. Indicated preterm birth was defined as delivery effected for maternal or fetal indications.

Umbilical cord blood was collected from 351 of the preterm infants by using an aseptic technique, including cleansing of the needle puncture site with alcohol. The cord blood was cultured for U urealyticum and M hominis as previously described,18 and it is these infants who are the focus of this study. Failure to collect cord blood cultures was generally caused by insufficient blood available after the routine clinical cord blood studies were obtained. Il-6 was assayed as previously reported.12 Values greater than 34.5 pg/mL, the 95th percentile of women who had an indicated preterm birth in this population, were considered elevated. The chorioamnionic space was cultured for U urealyticum and M hominis and other aerobic and anaerobic organisms as previously described.19 Membrane cultures for U urealyticum and M hominis as well as other organisms were available for all 351 of the placentas in which cord blood was available.

Placental histology for each of the 351 preterm neonates with cord blood cultures was available for study. In each case, a minimum of 2 membrane rolls, 2 complete sections of umbilical cord (1 from the placental and 1 from the fetal end of the cord), and 2-4 transmural parenchymal sections were submitted for routine histology. All cases were evaluated histologically by a single pathologist (O.F.-P.) using a placental evaluation protocol adapted from Bendon et al.20 For this study, the free membranes, chorionic plate, and umbilical cord were evaluated qualitatively for the presence of polymorphonuclear (PMN) infiltration. A PMN infiltration was considered present with PMNs in an essentially linear distribution. Specifically, scattered, entrapped, single, or sparsely distributed cells were not scored as an infiltration. The number of PMNs in an infiltration generally exceeded 20/high-power field (HPF 400×), but 5-10 or more/HPF were also scored as a PMN infiltration. The membranes, chorionic plate, and decidua basalis were evaluated for the presence of chronic lymphohistiocytic and plasmacytic inflammation, and the chorionic plate and cord for thrombosis.21, 22, 23, 24 The umbilical cord was evaluated for funisitis, defined as neutrophilic infiltrate in cord vessel walls and/or Wharton’s jelly. The decidua basalis was also evaluated for the presence of plasma cells, acute microfocal hemorrhages, and hemosiderin. In addition, the decidua basalis was evaluated for the presence of diffuse decidual leukocytoclastic necrosis, a bandlike distribution of coagulative necrosis variably admixed with a deeper region containing karyorrhectic debris.17

Neonatal outcome data through hospital discharge or death was also recorded. Neonatal systemic inflammatory response syndrome (SIRS) was defined as the presence of negative cerebrospinal fluid and blood cultures plus clinically suspected sepsis or a band: band + polymorphonuclear cell ratio of 0.15 or greater. The diagnoses of grade 3 or 4 intraventricular hemorrhage (IVH) or cystic periventricular leukomalacia (PVL) were made with the use of ultrasound criteria.25 Necrotizing enterocolitis (NEC) stage 2 or greater was considered present if diagnosed clinically by the neonatologist. Respiratory distress syndrome (RDS) was defined as the documentation of any of these 3 criteria: (1) infant oxygen requirement at 6 hours through 24 hours of life, (2) an abnormal chest radiograph consistent with RDS within the first 24 hours of life, and (3) need for surfactant. Bronchopulmonary dysplasia (BPD) was defined as infant oxygen requirement at 28 days and chronic lung disease as oxygen requirement at 36 weeks of life.

Data analyses were performed with SAS software (v 8;SAS Institute, Inc, Cary, NC). Frequencies and means between groups were compared with the use of χ2 tests for discrete variables and t tests and analysis of variance for continuous variables. Logistic regression analyses, adjusting for gestational age, race, and infant sex, were used to determine the odds ratio (OR) for a positive U urealyticum and/or M hominis culture to be associated with spontaneous preterm birth, various placental findings, and with the newborn outcomes SIRS and BPD. A P value ≤ .05 was chosen to define statistical significance. The study was approved by the University of Alabama-Birmingham Institutional Review Board.