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Contemporary cesarean delivery practice in the United States

Published:August 13, 2010DOI:https://doi.org/10.1016/j.ajog.2010.06.058

      Objective

      To describe contemporary cesarean delivery practice in the United States.

      Study Design

      Consortium on Safe Labor collected detailed labor and delivery information from 228,668 electronic medical records from 19 hospitals across the United States, 2002-2008.

      Results

      The overall cesarean delivery rate was 30.5%. The 31.2% of nulliparous women were delivered by cesarean section. Prelabor repeat cesarean delivery due to a previous uterine scar contributed 30.9% of all cesarean sections. The 28.8% of women with a uterine scar had a trial of labor and the success rate was 57.1%. The 43.8% women attempting vaginal delivery had induction. Half of cesarean for dystocia in induced labor were performed before 6 cm of cervical dilation.

      Conclusion

      To decrease cesarean delivery rate in the United States, reducing primary cesarean delivery is the key. Increasing vaginal birth after previous cesarean rate is urgently needed. Cesarean section for dystocia should be avoided before the active phase is established, particularly in nulliparous women and in induced labor.

      Key words

      Cesarean delivery has become the most common major surgical procedure in many parts of the world.
      • Villar J.
      • Valladares E.
      • Wojdyla D.
      • et al.
      Caesarean delivery rates and pregnancy outcomes: the 2005 WHO global survey on maternal and perinatal health in Latin America.
      • Lumbiganon P.
      • Laopaiboon M.
      • Gülmezoglu A.M.
      • et al.
      Method of delivery and pregnancy outcomes in Asia: the WHO global survey on maternal and perinatal health 2007-08.
      The national rate of cesarean delivery in the United States has increased more than 50% since 1996 to 31.8% in 2007.

      Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data for 2007. National Vital Statistics Reports, Web release; vol. 57 no. 12. Hyattsville, MD: National Center for Health Statistics. Released March 18, 2009.

      This upward trajectory appears likely to continue in the near future.
      For Editors' Commentary, see Table of Contents
      Reasons for the increase are multifaceted. Delayed childbearing, increasing maternal body mass, more multifetal gestations, and low use of vaginal birth after previous cesarean (VBAC) are commonly cited causes.
      • Joseph K.S.
      • Young D.C.
      • Dodds L.
      • et al.
      Changes in maternal characteristics and obstetric practice and recent increases in primary cesarean delivery.
      • Macones G.A.
      Clinical outcomes in VBAC attempts: what to say to patients?.
      Cesarean delivery on maternal request
      • Habiba M.
      • Kaminski M.
      • Da Fré M.
      • et al.
      Cesarean section of request: a comparison of obstetricians' attitudes in eight European countries.
      and physicians' fear of litigation due to a poor obstetric outcome
      • Murthy K.
      • Grobman W.A.
      • Lee T.A.
      • Holl J.L.
      Association between rising professional liability insurance premiums and primary cesarean delivery rates.
      may also be contributing to the escalating rate of cesarean delivery. Despite anecdotal evidence and the common belief that certain cesarean deliveries may be unnecessary, the magnitude of unnecessary cesarean section at the national level is unknown. Reliable, detailed information on labor and delivery is often unavailable in a large population. Consequently, our understanding of the underlying causes of high cesarean rate is incomplete.
      To meet this challenge, the Eunice Shriver Kennedy National Institute of Child Health and Human Development, National Institutes of Health, in collaboration with 12 institutions across the country, conducted a retrospective observational study entitled “the Consortium on Safe Labor.” The goal of the study was to collect comprehensive information on contemporary labor and delivery practice in multiple institutions. This paper describes the contemporary cesarean delivery practice in the US population.

      Materials and Methods

      The Consortium on Safe Labor included 12 clinical centers (with 19 hospitals) across 9 American College of Obstetricians and Gynecologists (ACOG) US districts. There were 8 university affiliated teaching hospitals, 9 teaching community hospitals, and 2 nonteaching community hospitals. They were chosen because of the availability of electronic medical records at each institution and because their geographic distribution covers all ACOG US districts. A total of 228,668 deliveries with 233,844 newborns between 2002 and 2008 were included in the study. Between 2005 and 2007, 87% births occurred. All births at 23 weeks or later in these institutions were included. A total of 9.5% of women contributed more than 1 delivery to the database. To avoid intraperson correlation, we selected the first delivery from each subject in the study, leaving 206,969 deliveries for analysis. Participating institutions extracted detailed information from their electronic medical records on maternal demographic characteristics, medical history, reproductive, and prenatal history, labor, and delivery summary, postpartum and newborn information. Information from the neonatal intensive care unit (NICU) was linked to the newborn records. Data on labor progression were extracted from the electronic labor database. Information on hospital and physician characteristics was collected from surveys of the local investigators, and maternal and newborn discharge summaries (in International Classification of Diseases-9 codes) were linked to each delivery. This project was approved by the institutional review boards of all participating institutions.
      Data transferred from the clinical centers were mapped to predefined common codes for each variable at the data coordinating center. Data inquiries, cleaning, recoding, and logic checking were performed. We also conducted validation studies for 4 key outcome diagnoses, including cesarean for nonreassuring fetal heart rate tracing, asphyxia, NICU admission for respiratory conditions, and shoulder dystocia. To validate data, eligible charts were selected, and investigators were asked to recollect data with chart abstraction done by hand. We compared the information hand collected from the medical charts with that downloaded from the electronic medical records. Appendix Table 1 indicates that most variables that were reviewed in this study are highly accurate. Although our records were not sampled randomly, the consistency among different records on the same variable (eg, singleton, gestational age, attempting vaginal birth, live birth, vertex presentation) indicates that the information provided in the validation studies is reliable and likely to be generalizable to the entire database. Thus, the electronic medical records are a reasonably accurate representation of the medical charts.
      Approximately 5.9% of women in our study had missing information on fetal presentation. Given the importance of fetal presentation in our analysis, we performed multiple imputation.
      • Rubin D.B.
      Multiple imputation for nonresponse in surveys.
      A logistic regression model imputed the likelihood of vertex/nonvertex presentation in a particular subject multiple times based on other obstetric characteristics, including maternal race, parity, previous uterine scar, number of fetus, external cephalic version, smoking, placenta previa, cephalopelvic disproportion, gestational age, reason for admission to labor/delivery, trial of labor, induction, fetal scalp electrode, operative vaginal delivery, and mode of delivery. When the imputed data were analyzed, the uncertainty that was related to imputation was taken into account.
      To make our study population reflect the overall US obstetric population and to minimize the impact of the various number of births from different institutions, we assigned a weight to each subject based on ACOG district, maternal race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and others), parity (nulliparous vs multiparous), and plurality (singleton vs multiple gestation). We first calculated the probability of each delivery with these 4 factors according to the 2004 National Natality data
      • Martin J.A.
      • Hamilton B.E.
      • Sutton P.D.
      • et al.
      Births: final data for 2004.
      ; publicly available National Natality data can no longer be separated by state after 2004. Then, based on the number of subjects each hospital contributed to the database, we assigned a weight to each subject. Appendix Table 2 indicates that the weighted study population is close to the entire US obstetric population. Therefore, we used the weighted sample throughout our analyses.
      We defined “attempting vaginal delivery or a trial of labor” as all vaginal deliveries plus cesarean deliveries with at least 2 vaginal examination data in the labor progression (or labor curve) database. For indications for cesarean delivery, we first listed all major indications and the percent of cesarean deliveries with a specific indication (1 woman may have more than 1 indication). “Elective cesarean delivery” was defined as cesarean for clinical indications of: (1) elective as denoted in the electronic medical record, (2) declining a trial of labor, and (3) a variety of factors that are not considered accepted indications for cesarean delivery such as elderly gravida, multiparity, remote from term, postterm/postdates, diabetes, chorioamnionitis, chronic or gestational hypertension without preeclampsia/eclampsia, premature rupture of the membranes, human papillomavirus infection, Group B streptococcus positive, polyhydramnios, fetal demise, tubal ligation, and social/religion concerns. We then grouped all indications into 3 hierarchical, mutually exclusive categories: “clinically indicated,” “mixed,” and “truly elective.” The “mixed” group included cesarean deliveries where not enough detailed information (eg, human immunodeficiency virus with an unknown viral load or unknown presentation of twins) was available to judge the necessity or where the clinical indications were not that strong (eg, preeclampsia).
      Duration of labor arrest was calculated as the duration of no appreciable change of cervical dilation in the first stage and the time interval between the first 10 cm and delivery in the second stage. “No appreciable change in cervical dilation” was defined as within 1 cm of change in dilation before delivery. All statistical analyses were performed using SAS version 9.1 (SAS Institute, Inc, Cary, NC). Given that this is a descriptive analysis with a very large sample size, no statistical testing was performed; nor were confidence intervals provided.

      Results

      The overall rate of cesarean delivery in our cohort was 30.5%, varying from 20% to 44% among the participating hospitals. Table 1 presents the overall and specific categories of cesarean delivery (primary vs repeat, and prelabor vs intrapartum) by maternal characteristics. With advancing maternal age, the overall cesarean rate doubled from 21.0% at age <20 years to 42% in women 35 years or older, mainly due to repeat, prelabor cesarean deliveries. Obesity was associated with substantially higher cesarean rates in all categories. One in 3 nulliparous women was delivered by cesarean section (31.2%). Multiparous women had an overall cesarean rate similar to that of nulliparous women (30.0%), primarily due to prelabor, repeat cesarean delivery.
      TABLE 1Cesarean rate by maternal characteristics and type of cesarean delivery
      VariableProportion of the population, %Overall cesarean rate,
      Overall cesarean rate = primary + repeat cesarean rates = prelabor + intrapartum cesarean rates. Repeat cesarean section includes cesarean section after previous myomectomy in nulliparous women (0.1%).
      %
      Primary cesarean delivery,
      Overall cesarean rate = primary + repeat cesarean rates = prelabor + intrapartum cesarean rates. Repeat cesarean section includes cesarean section after previous myomectomy in nulliparous women (0.1%).
      %
      Repeat cesarean delivery,
      Overall cesarean rate = primary + repeat cesarean rates = prelabor + intrapartum cesarean rates. Repeat cesarean section includes cesarean section after previous myomectomy in nulliparous women (0.1%).
      %
      Prelabor cesarean delivery,
      Overall cesarean rate = primary + repeat cesarean rates = prelabor + intrapartum cesarean rates. Repeat cesarean section includes cesarean section after previous myomectomy in nulliparous women (0.1%).
      %
      Intrapartum cesarean delivery,
      Overall cesarean rate = primary + repeat cesarean rates = prelabor + intrapartum cesarean rates. Repeat cesarean section includes cesarean section after previous myomectomy in nulliparous women (0.1%).
      %
      n (unweighted)206,96960,86638,33622,53032,38028,486
      n (weighted)3,997,4361,220,877727,941492,935696,583524,294
      Maternal age, y
       <208.621.018.82.26.614.5
       20-2422.624.616.58.111.712.9
       25-2927.028.116.611.515.912.3
       30-3424.733.618.914.920.613.2
       35+17.242.221.720.528.314.0
      Race/ethnicity
       Non-Hispanic white56.629.918.311.617.812.1
       Non-Hispanic black14.233.420.513.217.416.3
       Hispanic22.930.316.513.816.913.4
       Asian/Pacific Islanders3.230.619.611.115.515.2
       Other3.129.317.411.817.212.1
      Health insurance
       Private53.531.319.312.017.913.4
       Public33.331.618.113.617.913.8
       Other/unknown13.224.614.010.614.210.3
      Body mass index at delivery, kg/m2
       <2513.522.314.08.413.88.6
       25.0-29.937.725.615.89.814.511.1
       30.0-34.927.632.619.313.318.414.3
       35.0+21.243.724.619.225.018.8
      Parity
       Nulliparous40.431.231.20.19.721.5
       Multiparous59.630.09.420.622.77.4
      Number of fetuses
       Singleton98.329.917.712.216.913.1
       Multiple1.765.947.018.950.615.3
      Labor induction in women attempting vaginal delivery
       No56.211.89.12.7011.8
       Yes43.821.119.51.6021.1
      Previous uterine scar
       No84.921.121.107.813.2
       Yes15.183.62.281.471.312.3
      Vertex presentation (singleton only)
       No5.192.871.121.673.819.0
       Yes94.926.614.911.713.812.8
      Hospital type
       University affiliated teaching hospital60.732.919.413.519.513.5
       Teaching community Hospital35.927.216.710.514.512.8
       Nonteaching community hospital3.423.112.810.412.610.5
      Zhang. Contemporary cesarean delivery practice in the US. Am J Obstet Gynecol 2010.
      a Overall cesarean rate = primary + repeat cesarean rates = prelabor + intrapartum cesarean rates. Repeat cesarean section includes cesarean section after previous myomectomy in nulliparous women (0.1%).
      A total of 65.9% multifetal gestations were delivered by cesarean section (in comparison to 29.9% in singleton pregnancies), and a majority of multifetal gestations did not attempt vaginal delivery. The induction rate was 36.2%, using all deliveries as the denominator, or 43.8% among women attempting vaginal delivery. The cesarean rate was twice as high in induced labor than in spontaneous labor in all pregnancies (21.1% vs 11.8%) and in singleton nulliparous women with vertex presentation (31.4% vs 14.2%). In women with a previous uterine scar, 28.8% had a trial of labor. Among them, the rate of successful VBAC was 57.1%. Overall, 83.6% of women with a uterine scar were delivered by cesarean section. A total of 92.8% fetuses with nonvertex presentation were delivered by cesarean section.
      To further examine the relative contribution of obstetric factors to the cesarean rate, we grouped the women into 7 categories according to the classification scheme proposed by Robson.
      • Robson S.M.
      Can we reduce the cesarean section rate?.
      Table 2 indicates that term pregnancies with a vertex, singleton fetus, and previous uterine scar contributed the most cesarean deliveries in the United States (30.9%), followed by term gestations with a singleton, vertex fetus whose labor was induced (19.2%). Multifetal gestations and pregnancies with nonvertex presentation accounted for only 6.7% of all births but contributed to one-fifth of all cesarean deliveries.
      TABLE 2Relative contribution of obstetric factors
      Robson classification
      Based on classification scheme proposed by Robson.10
      Obstetric characteristicsProportion of all deliveries, %Rate of prelabor cesarean delivery, %Rate of intrapartum cesarean delivery, %Proportion of all cesarean deliveries, %
      1Nulliparous, singleton, vertex, ≥37 wk, spontaneous labor16.514.88.0
      3Multiparous, singleton, vertex, ≥37 wk, no uterine scar, spontaneous labor20.93.12.1
      2a + 4aAll women, singleton, vertex, ≥37 wk, no uterine scar, induced labor30.919.019.2
      2b + 4bAll women, singleton, vertex, ≥37 wk, no uterine scar, prelabor cesarean delivery2.41007.9
      5All women, singleton, vertex, ≥37 wk, uterine scar11.570.211.830.9
      10All women, singleton, vertex, <37 wk, regardless uterine scar11.121.514.213.0
      6 + 7 + 8 + 9All women, multiple gestation or nonvertex presentation, regardless uterine scar6.767.717.918.8
      Overall100%100%
      Zhang J. Contemporary cesarean delivery practice in the US. Am J Obstet Gynecol 2010.
      a Based on classification scheme proposed by Robson.
      • Robson S.M.
      Can we reduce the cesarean section rate?.
      The main indication for prelabor cesarean delivery was previous uterine scar, followed by fetal malpresentation (Table 3). Among intrapartum cesarean deliveries, approximately half of them were performed for “failure to progress” or “cephalopelvic disproportion,” and more than a quarter were performed for indications of nonreassuring fetal testing or fetal distress. “Truly elective” cesarean delivery accounted for 9.6% of prelabor and 2.1% of intrapartum cesarean deliveries As some prelabor cesarean deliveries in the “mixed” group were eligible for a trial of labor (eg, single previous low transverse cesarean section and vertex-vertex twin gestation), the “truly elective” cases may be an underestimate in the current study.
      TABLE 3Main recorded indications for cesarean delivery
      IndicationPrelabor cesarean delivery, %Intrapartum cesarean delivery, %
      Individual indications
      Women may have more than 1 indication. The total percentage may exceed 100%;
       Previous uterine scar45.18.2
       Failure to progress/cephalopelvic disproportion2.047.1
       Elective
      Indications for elective cesarean delivery include “elective”, declining trial of labor, elder gravid, multiparity, remote from term, postterm/postdates, diabetes, chorioamnionitis, chronic or gestational hypertension without preeclampsia/eclampsia, premature rupture of the membranes, human papillomavirus infection, Group B streptococcus positive, polyhydramnios, fetal demise, tubal ligation, and social/religion concerns;
      26.411.7
       Nonreassuring fetal testing/fetal distress6.527.3
       Fetal malpresentation17.17.5
       Hypertensive disorders3.11.6
       Fetal macrosomia3.31.2
       Multiple gestation2.80.8
      Grouped indications (hierarchical, mutually exclusive)
       Clinically indicated
      Clinically indicated includes emergency, non-reassuring fetal heart rate tracing/fetal distress, failure to progress, cephalopelvic disproportion, failed induction, failed forceps, failed vaginal birth after previous cesarean, placenta abruption, placenta previa, shoulder dystocia, and history of shoulder dystocia;
      9.774.9
       Mixed
      Mixed includes: previous uterine scar, breech/malpresentation, fetal anomalies, fetal macrosomia, human immunodeficiency virus infection, multiple gestation, preeclampsia/eclampsia, other;
      80.723.0
       Truly elective
      Truly elective: without any indication in the “clinically indicated” or “mixed” categories.
      9.62.1
       Total100100
      Zhang. Contemporary cesarean delivery practice in the US. Am J Obstet Gynecol 2010.
      a Women may have more than 1 indication. The total percentage may exceed 100%;
      b Indications for elective cesarean delivery include “elective”, declining trial of labor, elder gravid, multiparity, remote from term, postterm/postdates, diabetes, chorioamnionitis, chronic or gestational hypertension without preeclampsia/eclampsia, premature rupture of the membranes, human papillomavirus infection, Group B streptococcus positive, polyhydramnios, fetal demise, tubal ligation, and social/religion concerns;
      c Clinically indicated includes emergency, non-reassuring fetal heart rate tracing/fetal distress, failure to progress, cephalopelvic disproportion, failed induction, failed forceps, failed vaginal birth after previous cesarean, placenta abruption, placenta previa, shoulder dystocia, and history of shoulder dystocia;
      d Mixed includes: previous uterine scar, breech/malpresentation, fetal anomalies, fetal macrosomia, human immunodeficiency virus infection, multiple gestation, preeclampsia/eclampsia, other;
      e Truly elective: without any indication in the “clinically indicated” or “mixed” categories.
      The cesarean rate was higher at the earlier gestational ages of delivery (Figure 1). For example, the cesarean delivery rate was over 60% at 28 weeks gestation and declined gradually with advancing gestation. In nulliparous women, intrapartum cesarean deliveries constituted the majority of cesarean sections at term (≥37 weeks). Among multiparous women, most cesarean deliveries occurred before the onset of labor across all gestational ages. Unlike in most women, the cesarean rate in women with a uterine scar did not decline with advancing gestation until 40 weeks.
      Figure thumbnail gr1
      FIGURE 1Cesarean delivery rate by gestational age
      Cesarean delivery rate by type of cesarean (prelabor vs intrapartum), gestational age and parity (nulliparous women, multiparous women, and women with a uterine scar).
      Zhang. Contemporary cesarean delivery practice in the US. Am J Obstet Gynecol 2010.
      We further examined the timing of cesarean delivery relative to cervical dilation among those women with vertex, singleton gestation attempting vaginal delivery (Figure 2). Induced labor was associated with twice as many cesarean deliveries as spontaneous labor in both nulliparous and multiparous women before and after 39 weeks, and the cesarean section was performed earlier in terms of cervical dilation in induced labor than in spontaneous labor. The cesarean rate was substantially higher in women with a uterine scar (47% and 33% before and after 39 weeks, respectively), and the cesarean section was performed at lower cervical dilation before 39 weeks than after 39 weeks.
      Figure thumbnail gr2
      FIGURE 2Cervical dilation at cesarean delivery
      Cervical dilation at intrapartum cesarean delivery among women attempting vaginal delivery by parity, onset of labor (induced vs spontaneous onset), previous uterine scar in singleton gestations.
      Zhang. Contemporary cesarean delivery practice in the US. Am J Obstet Gynecol 2010.
      Table 4 presents total duration of labor arrest before intrapartum cesarean delivery for “failure to progress,” “cephalopelvic disproportion,” or “failed induction” among singleton, vertex presentation with, and without a uterine scar. The duration of labor arrest declined as labor advanced. At 4 cm of cervical dilation, for example, the median duration for nulliparous women was 4 hours and less than 3 hours at 6 cm. The duration was similar between spontaneous and induced labors. However, nearly half of cesarean sections were performed before 6 cm in induced labor and in women with a previous uterine scar. One-third of cesarean deliveries at the second stage were performed at less than 3 hours in nulliparous women, whereas, a quarter were performed at less than 2 hours in multiparous women.
      TABLE 4Duration of labor arrest (in hours) prior to intrapartum cesarean for “failure to progress/cephalopelvic disproportion” or “failed induction”
      Cervical dilation at cesarean section, cmNulliparous womenMultiparous womenWomen with a previous uterine scar having a trial of labor, median (cumulative percentage)
      Spontaneous labor, median (cumulative percentage)Induced labor, median (cumulative percentage)Spontaneous labor, median (cumulative percentage)Induced labor, median (cumulative percentage)
      013.8 (0.3)14.5 (4)— (0.1)16.0 (2)9.6 (2)
      110.0 (2)9.4 (10)— (1)11.7 (6)6.3 (6)
      26.8 (3)5.6 (15)— (3)8.6 (9)6.5 (16)
      34.0 (7)4.3 (23)6.9 (6)5.5 (16)5.0 (21)
      44.0 (17)4.0 (40)2.7 (14)3.4 (29)2.5 (36)
      53.5 (28)3.2 (53)4.0 (19)2.4 (44)2.8 (49)
      62.9 (38)2.8 (63)3.6 (31)2.5 (54)3.2 (62)
      72.8 (46)2.2 (69)2.8 (39)2.6 (63)2.4 (69)
      83.0 (56)2.6 (75)2.8 (53)2.9 (71)2.0 (75)
      92.2 (65)2.3 (81)2.8 (69)1.7 (83)1.3 (84)
      Second stage3.8 (100)3.5 (100)2.9 (100)2.8 (100)2.3 (100)
      Among the second stage cesarean deliveries (cumulative percentage)
       <2 h1214242739
       2-3 h3335556356
       3-4 h5563748176
       ≥4 h100100100100100
      —, the number of subjects is too small to have a meaningful value.
      Zhang. Contemporary cesarean delivery practice in the US. Am J Obstet Gynecol 2010.

      Comment

      Our study is a large, contemporary assessment of cesarean delivery practice for the US obstetric population. We found that:
      • One in 3 nulliparous women was delivered by cesarean section.
      • Prelabor repeat cesarean delivery due to a previous uterine scar was the most common reason for cesarean section, contributing almost a third of all cesarean deliveries. In contrast, the rate of trial of labor is disappointingly low, and the associated success rate for vaginal birth has declined.
      • Approximately 44% of women attempting vaginal delivery had induced labor, and that within this group the cesarean rate was twice as high as in women with spontaneous labor.
      • A high percentage of intrapartum cesarean deliveries were performed before 6 cm of cervical dilation, particularly in nulliparous women, induced labor, and women attempting VBAC.

      VBAC

      The VBAC rate experienced precipitous decline since 1996, which coincided with an over 50% increase in cesarean rate during the same period.

      Hamilton BE, Martin JA, Ventura SJ. Births: preliminary data for 2007. National Vital Statistics Reports, Web release; vol. 57 no. 12. Hyattsville, MD: National Center for Health Statistics. Released March 18, 2009.

      Our study indicates that prelabor repeat cesarean sections currently have a profound impact on the overall cesarean rate. Some experts estimate that two-thirds of women with a uterine scar are eligible for a trial of labor.
      • Landon M.B.
      Vaginal birth after cesarean delivery.
      Yet, the rate of trial of labor is quite low in the United States. In 1999-2002, Landon et al
      • Landon M.B.
      • Hauth J.C.
      • Leveno K.J.
      • et al.
      Maternal and perinatal outcomes associated with a trial of labor after prior cesarean delivery.
      reported a rate of 38.9% in a NICHD Maternal-Fetal Medicine Unit Research Network study. The rate of trial of labor declined significantly from 48.3% in 1999 to 30.7% in 2002. This is consistent with our finding that the rate was 28.8% in 2005-2007, and ours may be an overestimate for the national level because academic institutions are overrepresented in our study. The low rate of trial of labor has been attributed in part to a slight increase in absolute risks of maternal and neonatal morbidity, professional liability concerns and physician and patient's attitude toward VBAC.
      • Macones G.A.
      Clinical outcomes in VBAC attempts: what to say to patients?.
      The recent change in ACOG recommendations also has reduced the availability of VBAC services in many hospitals.
      • Roberts R.G.
      • Deutchman M.
      • King V.J.
      • Fryer G.E.
      • Miyoshi T.J.
      Changing policies on vaginal birth after cesarean: impact on access.
      The success rate of attempted VBAC in our study was markedly lower (57.1%) than that in previous large studies. Lieberman et al
      • Lieberman E.
      • Ernst E.K.
      • Rooks J.P.
      • Stapleton S.
      • Flamm B.
      Results of the national study of vaginal birth after cesarean in birth centers.
      noted a VBAC success rate of 87% in 41 birth centers in 1990-2000. Macones et al
      • Macones G.A.
      • Peipert J.
      • Nelson D.B.
      • et al.
      Maternal complications with vaginal birth after cesarean delivery: a multicenter study.
      found a success rate of 75.5% in a regional study with 17 hospitals in 1996-2000, similar to that found by Landon et al
      • Landon M.B.
      • Hauth J.C.
      • Leveno K.J.
      • et al.
      Maternal and perinatal outcomes associated with a trial of labor after prior cesarean delivery.
      (73.4%). Gregory et al,
      • Gregory K.D.
      • Korst L.M.
      • Fridman M.
      • et al.
      Vaginal birth after cesarean: clinical risk factors associated with adverse outcome.
      using 2002 California hospital discharge data, reported an overall success rate of 67%. One possible explanation of our finding is that the success rate of attempted VBAC is more recently influenced by other factors. Physicians and patients may be less committed even during a trial of labor.
      • Kalish R.B.
      • McCullough L.
      • Gupta M.
      • Thaler H.T.
      • Chervenak F.A.
      Intrapartum elective cesarean delivery: a previously unrecognized clinical entity.
      For instance, half of the intrapartum cesarean sections for dystocia were performed before 6 cm of cervical dilation in our study. Many women may not be in active phase before that time.
      • Zhang J.
      • Troendle J.
      • Mikolajczyk R.
      • Sundaram R.
      • Beaver J.
      • Fraser W.
      The natural history of the normal first stage of labor.
      The frequency of oxytocin use for labor augmentation in the trial of labor was one-sixth of that in multiparous women without a uterine scar.
      Another possible reason for the low success rate may be related to our definition of “a trial of labor.” A woman with a uterine scar, minimal dilation, and 2 pelvic examinations recorded in the labor database would have been considered a trial of labor. Such cases may have increased the VBAC rate but reduced the success rate. However, findings of vaginal examinations that were entered in the labor progression (labor curve) computer system on the labor floor are often an indication for intended vaginal delivery. Thus, the above scenario may not have substantially affected our results.

      Induction of labor

      In parallel with the increasing cesarean rate, the rate of labor induction also has increased significantly in many developed countries, including a doubling of the US rate between 1990-2000 (from 9.5% in 1990 to 20.2% in 2000, and 22.6% in 2006).
      • Martin J.A.
      • Hamilton B.E.
      • Sutton P.D.
      • et al.
      Births: final data for 2006.
      In comparison, the overall induction rate was 35.2% in our study (around 2006); the induction rate in women attempting vaginal delivery was 43.8%. These findings suggest that the national figures based on birth certificates may have been an underestimate of the true national induction rate.
      • Roberts C.L.
      • Bell J.C.
      • Ford J.B.
      • Morris J.M.
      Monitoring the quality of maternity care: how well are labour and delivery events reported in population health data?.
      For medically indicated induction of labor, the benefits for the mother and/or the fetus are indisputable. However, controversies arise when labor is induced for women with absent or marginal clinical indications.
      • Vahratian A.
      • Zhang J.
      • Troendle J.F.
      • Sciscione A.C.
      • Hoffman M.K.
      Labor progression and risk of cesarean delivery in electively induced nulliparas.
      • Grobman W.A.
      Elective induction: when? Ever?.
      • Nicholson J.M.
      • Parry S.
      • Caughey A.B.
      • Rosen S.
      • Keen A.
      • Macones G.A.
      The impact of the active management of risk in pregnancy at term on birth outcomes: a randomized clinical trial.
      Our data show that induced labor was twice as likely to result in cesarean delivery than spontaneous labor. Half of cesarean sections for dystocia in induced labor were performed before 6 cm of dilation, suggesting that clinical impatience may play a role in decision making. Some studies also suggest that induction of labor increases the risk of postpartum hemorrhage and blood transfusion.
      • Grobman W.A.
      Elective induction: when? Ever?.
      Therefore, although more research is warranted, caution is needed to perform elective labor induction, as it may result in maternal morbidity and repeat cesarean deliveries in subsequent pregnancies.

      Timing of intrapartum cesarean delivery

      The high proportion of intrapartum cesarean deliveries performed before 6 cm of cervical dilation is concerning, particularly in nulliparous women and in induced labor. The active phase of labor is typically considered starting at 4 cm of dilation.
      • Albers L.L.
      • Schiff M.
      • Gorwoda J.G.
      The length of active labor in normal pregnancies.
      • Rouse D.J.
      • Owen J.
      • Hauth J.C.
      Active-phase labor arrest: oxytocin augmentation for at least 4 hours.
      However, a recent study showed that multiparous women may not start the active phase until 6 cm, whereas, nulliparous women may not have a typical active phase of labor.
      • Zhang J.
      • Troendle J.
      • Mikolajczyk R.
      • Sundaram R.
      • Beaver J.
      • Fraser W.
      The natural history of the normal first stage of labor.
      In contemporary nulliparous women who had vaginal delivery and normal perinatal outcome, labor may not progress for 6 hours at 4 cm or 3 hours at 5 cm of dilation (results not shown). In the current study, the median duration of labor arrest in nulliparous women, including periods before and after any intervention, was 4 hours at 4 cm. Thus, a cesarean section for dystocia before 6 cm in nulliparous women appears too soon in some cases.
      We also found that one-third of cesarean deliveries at the seond stage were performed at less than 3 hours in nulliparous women, whereas, a quarter were performed at less than 2 hours in multiparous women. This is of concern because ACOG guidelines define arrest of descent as greater than 3 hours in nulliparous women with epidural analgesia and greater than 2 hours in multiparous women with epidural analgesia.
      American College of Obstetricians and Gynecologists
      Dystocia and augmentation of labor ACOG practice bulletin no. 49.
      Given that 90% of the subjects used epidural analgesia and that the median duration in the second stage arrest included “decision-to-incision” time, the true waiting period in the second stage arrest appears shorter than ACOG recommendations in many cesarean cases.
      It should be noted that even though we selected 12 institutions across 9 ACOG districts, our study subjects were not a random sample of all births in the United States. Academic institutions are overrepresented in our cohort. This may in part explain why our weighted preterm birth rate was higher (14.1%) than the national average (12.8% in 2006)
      • Martin J.A.
      • Hamilton B.E.
      • Sutton P.D.
      • et al.
      Births: final data for 2006.
      and why the induction rate in our study was higher than the published national average. Yet, our overall cesarean rate was slightly lower than the corresponding national average (30.5% vs 31.1% in 2006).
      • Martin J.A.
      • Hamilton B.E.
      • Sutton P.D.
      • et al.
      Births: final data for 2006.
      Nonetheless, for the first time we were able to separate cesarean delivery by prelabor and intrapartum in a large multicenter study. Our study provides detailed information on when cesarean section was performed, allowing us to identify potential areas for optimal management.
      In summary, our study shows that 1 in 3 nulliparous women is delivered by cesarean section, which has a tremendous impact on subsequent prelabor repeat cesarean delivery. Prelabor repeat cesarean delivery now contributes almost a third of all cesarean deliveries. To make a significant impact on the high cesarean delivery rate in the United States, the focus should be preventing unnecessary primary cesarean deliveries from several aspects. First, we need to decrease the rate of cesarean delivery associated with a high rate of induction of labor. Cesarean section for dystocia should be avoided before active phase of labor is established particularly in nulliparous women, induced labor, and VBAC attempts. Second, there should be a clinically accepted indication for performing cesarean delivery. Finally, increasing access to and patient education on trial of labor in women with a previous uterine scar and improving the success rate are urgently needed.

      Appendix

      TABLE 1Validity of data from electronic medical records comparing to medical charts in selected variables
      Sample selection criteriaInformation from the electronic medical recordsConcordant with medical chart, %Disagreed with medical chart, %Not found in medical chart, %
      Nulliparous, singleton, live, vertex fetus at admission, Attempting vaginal delivery and cesarean delivery due to non-reassuring fetal heart rate tracing (n = 5662)Nulliparity99.10.90.0
      Live fetus at admission99.90.10.0
      Attempting vaginal delivery96.23.60.2
      Singleton98.50.11.4
      Vertex at admission96.71.12.2
      Cesarean delivery99.90.10.0
      Primary indication for cesarean delivery: nonreassuring fetal heart rate tracing/fetal distress93.33.53.2
      Singleton, gestational age ≥34 wk, attempting vaginal delivery, had an Apgar score at 5 min <4 or umbilical cord pH <7.0 or base deficit ≥12 mmol/L (n = 503)Singleton99.800.2
      Gestational age ≥34 wk97.62.40
      Attempting vaginal delivery95.83.80.4
      Apgar score at 5 min <4 or umbilical cord pH <7.0 or base deficit ≥12 mmol/L94.05.20.8
      Liveborn, gestational age ≥34 wk, admitted to NICU or special care nursery for respiratory conditions (n = 4641)Livebirth99.70.10.2
      Gestational age ≥34 wk97.32.60.1
      Admitted to NICU or special care nursery97.42.20.4
      Singleton, gestational age ≥37 wk, vertex presentation, clinical diagnosis of shoulder dystocia, no antepartum fetal death, no fetal anomaly (n = 2640)Singleton98.80.01.2
      Gestational age ≥37 wk98.70.21.1
      Vertex at admission94.40.55.1
      Clinical diagnosis of shoulder dystocia91.97.80.3
      No antepartum fetal death95.90.73.4
      No fetal anomaly96.10.33.6
      NICU, neonatal intensive care unit.
      Zhang. Contemporary cesarean delivery practice in the US. Am J Obstet Gynecol 2010.
      TABLE 2Description of the study population in comparison to the 2004 US birth cohort
      CharacteristicsCSL cohort (Nonweighted)CSL cohort (Weighted)US birth cohort
      2006 National Natality data;18
      No. of women206,9693,997,4364,018,091
      Race/ethnicity,
      These factors plus American College of Obstetricians and Gynecologists district were used to create sample weights.
      %
       Non-Hispanic white495757
       Non-Hispanic black221414
       Hispanics172323
       Asian/Pacific Islander435
       Other/unknown831
      Nullipara,
      These factors plus American College of Obstetricians and Gynecologists district were used to create sample weights.
      %
      444040
      Multifetal gestation,
      These factors plus American College of Obstetricians and Gynecologists district were used to create sample weights.
      %
      2.31.71.7
      Maternal age, y (mean)27.628.127.4
      Cesarean delivery, %29.430.531.1
      Gestational age, wk (mean)38.238.138.6
      Preterm birth, % (<37 wk)13.014.112.8
      CSL, The Consortium on Safe Labor.
      Zhang. Contemporary cesarean delivery practice in the US. Am J Obstet Gynecol 2010.
      a 2006 National Natality data;
      • Zhang J.
      • Troendle J.
      • Mikolajczyk R.
      • Sundaram R.
      • Beaver J.
      • Fraser W.
      The natural history of the normal first stage of labor.
      b These factors plus American College of Obstetricians and Gynecologists district were used to create sample weights.

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