Cesarean delivery is the most common major surgical procedure performed in the United States.1 The total cesarean delivery rate, defined as the percentage of cesarean deliveries out of all births in a given year, has increased dramatically since 1996; in 2009, 32.9% of all U.S. deliveries were cesarean.2 The United States has one of the highest cesarean delivery rates in the world.3 Cesarean delivery is associated with higher morbidity and mortality than vaginal births.4 Cesarean delivery also increases the risk of subsequent uterine rupture, placenta accreta, hemorrhage, hysterectomy, and maternal death.5,6 Safely lowering the total cesarean delivery rate is a stated objective of the U.S. Department of Health and Human Services.7
Similar to the total cesarean delivery rate, the primary cesarean delivery rate, defined as the percentage of cesarean deliveries out of all births to women who have not had a previous cesarean delivery, also has increased. In 1996, the U.S. primary cesarean delivery rate was 14.5%, whereas in 2007 it was 23.4%—an increase of more than 60%.8 The primary cesarean delivery rate has become a major driver in the total cesarean delivery rate. Using data from the Consortium on Safe Labor, Zhang et al9 found that having a previous uterine scar contributed most to the overall cesarean delivery rate, accounting for 30.9% of all cesarean deliveries. Barber et al10 found that 50% of the increase in cesarean deliveries at their institution was attributed to an increase in primary cesarean deliveries. Understanding the factors leading to primary cesarean deliveries is essential to reducing the total cesarean delivery rate.
Many factors have been cited for the increase in cesarean delivery rate, including delayed childbearing, multiple gestations, increasing maternal obesity, maternal request, and physician's fear of litigation.11–14 The majority of U.S. studies to quantify these factors have been limited by sample size or geography; the contribution of factors on a national scale is unclear. The objectives of this study were to characterize the indications for primary cesarean delivery in a large national cohort and to identify opportunities to lower the U.S. primary cesarean delivery rate.
MATERIALS AND METHODS
The current study examined a subset of the data collected by the Consortium on Safe Labor, a large, multisite, retrospective cohort study of contemporary labor and delivery practice. The Consortium on Safe Labor collected detailed information from electronic medical records of 228,562 deliveries at 23 weeks of gestation or more from 12 clinical centers, including 19 hospitals, from 2002 to 2008. Centers were selected based on numerous criteria, including their geographic location (nine states and the District of Columbia), which encompassed nine American Congress of Obstetricians and Gynecologists districts, and their use of electronic medical records. The centers transferred data to a data coordinating center, where the data were mapped to common categories for predefined variables. Data inquiries, cleaning, and logic checking were performed by the data coordinating center. Validation studies confirmed a high level of accuracy. Concordance with the medical chart was more than 95% for 16 of 20 variables examined; the lowest concordance was 91.1% for the clinical diagnosis of shoulder dystocia.9
The data coordinating center mapped the indications for primary cesarean delivery into 15 predefined categories as follows: failure to progress (arrest of dilation in the first stage of labor or arrest of descent in the second stage of labor) and cephalopelvic disproportion; nonreassuring fetal heart rate (FHR) tracing and fetal distress; fetal malpresentation; suspected fetal macrosomia; preeclampsia and eclampsia; chorioamnionitis; fetal anomaly; multiple gestation; obstetric factors (uterine rupture, cord prolapse, placenta previa, vasa previa, abruption, or other obstetric emergency); previous uterine scar (including hysterotomy or myomectomy); human immunodeficiency virus and herpes simplex virus; history of shoulder dystocia; shoulder dystocia this pregnancy; elective; and other. Indications in the elective category included maternal request, multiparity, women desiring a tubal ligation, advanced maternal age, diabetes mellitus, human papilloma virus, postterm or postdates, pregnancy remote from term, group B streptococcus, polyhydramnios, fetal death, and social or religious concerns. Other indications included all maternal factors not elsewhere specified.
To obtain the cohort for this study, the 228,562 deliveries in the Consortium on Safe Labor database were limited to first-recorded deliveries (n=208,695) to avoid intraperson correlation. Women who had a vaginal delivery (n=142,592) or underwent a repeat cesarean delivery (n=27,619) were excluded, leaving 38,484 women who had a primary cesarean delivery as the study sample.
We further examined the timing of delivery relative to the first and second stages of labor. For any woman who had failure to progress or cephalopelvic disproportion as an indication for cesarean delivery, dilation at the last recorded cervical examination was noted. For any woman who had arrest of descent, the time between full dilation and birth of the neonate was recorded and a note was made about any attempted trial of operative vaginal delivery. Other potential factors for a primary cesarean delivery also were explored in more detail, including fetal presentation in twin gestations and the actual birth weight of any neonate for whom a cesarean delivery was performed for suspected fetal macrosomia. For women who underwent labor induction, we calculated the simplified Bishop score as described by Laughon et al15 using the recorded cervical examination from admission.
We grouped the indications for primary cesarean delivery into the following three hierarchical, mutually exclusive categories using the criteria of Zhang et al9: clinically indicated; mixed; and truly elective. In cases in which more than one reason for cesarean delivery was given, and when the reasons straddled categories, the delivery was placed in the higher ranking category in which clinically indicated outranked mixed, which, in turn, outranked truly elective.
We stratified the results by parity and, for primiparous women, we further stratified the results into deliveries at term (37 weeks of gestation and beyond) with a singleton in cephalic presentation. All analyses were performed using SAS 9.1.3. Although this study is primarily descriptive, the χ2 test was used to compare the characteristics of primiparous and multiparous women, with P<.05 considered statistically significant.
Of the 38,484 records in our cohort, 76 (0.20%) lacked information about maternal age, 1,700 (4.4%) lacked mother's race or ethnicity, and 7,843 (20.4%) lacked data regarding body mass index. Birth weight was missing for 514 cases (1.3%), including three charts stating that the indication for cesarean delivery was suspected fetal macrosomia. Sufficient data to calculate a simplified Bishop score were unavailable for 5,365 women (36.2%) who underwent labor induction, and no cervical examination was documented for 945 women (6.9%) who underwent a primary cesarean delivery for labor arrest. The length of the second stage of labor could not be calculated for 329 women (11.3%) with a diagnosis of arrest of descent. For each variable, we compared demographics, medical histories, and labor characteristics of women for whom the variable was available and those for whom it was missing. Although some differences were statistically significant, we concluded that there were no clinically significant differences.
The Institutional Review Boards of all participating institutions, the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and the data coordinating center (The EMMES Corporation, Rockville, Maryland) approved the Consortium on Safe Labor project. The MedStar Washington Hospital Center Institutional Review Board approved the current analysis of primary cesarean delivery using Consortium on Safe Labor data.
Of the 38,484 women in the study cohort, 28,116 (73.1%) were primiparous and 10,368 (27.0%) were multiparous. The overall primary cesarean delivery rate was 21.3% (38,484 out of 181,076). Among the 91,208 primiparous women in the Consortium on Safe Labor database, 28,116 had a cesarean delivery and 63,092 had a vaginal delivery; thus, the primary cesarean delivery rate for primiparous women was 30.8% (28,116 out of 91,208). Among the 89,868 multiparous women who had not had a previous cesarean delivery, 10,368 had a cesarean delivery and 79,500 had a vaginal delivery; thus, the primary cesarean delivery rate for multiparous women was 11.5% (10,368 out of 89,868).
The demographic characteristics of women who had a primary cesarean delivery differed by parity (Table 1). Primiparous women were more likely to be younger, thinner, and have private health insurance than multiparous women; they also were more likely to be non-Hispanic white. The medical histories and labor characteristics of women who had a primary cesarean delivery also differed by parity. Primiparous women were more likely to have hypertension and to be undergoing labor induction, whereas multiparous women were more likely to have diabetes mellitus, to have a multiple gestation, and to deliver preterm.
The most common indications for primary cesarean delivery were failure to progress (35.4%), nonreassuring FHR tracing (27.3%), and fetal malpresentation (18.5%), although frequencies for each indication varied by parity (Table 2). For primiparous women, failure to progress was the most common indication (41.3%), followed by nonreassuring FHR tracing (23.4%) and fetal malpresentation (15.8%). For multiparous women, the most common indication was fetal malpresentation (25.8%), followed by nonreassuring FHR tracing (24.6%) and failure to progress (19.5%).
Among women who had a primary cesarean delivery for failure to progress, 42.6% of primiparous women and 33.5% of multiparous women never progressed beyond 5 cm of dilation before delivery (Table 3). Among women with a primary cesarean delivery who reached the second stage of labor, 17.3% underwent cesarean delivery for arrest of descent before 2 hours and only 1.1% were given a trial of operative vaginal delivery (Table 4). Among women who had a primary cesarean delivery for suspected fetal macrosomia, 97.3% of neonates had an actual birth weight of less than 5,000 g, 80.3% weighed less than 4,500 g, and 41.9% weighed less than 4,000 g.
Of the 91,208 primiparous women in the Consortium on Safe Labor database, 69,485 were at term with a singleton gestation in cephalic presentation; 17,531 of these women underwent a primary cesarean delivery, yielding a primary cesarean delivery rate of 25.2%. Primiparous women at term with a singleton gestation in cephalic presentation contributed 45.6% of the primary cesarean deliveries in the study cohort (17,531 out of 38,484). The top three indications for primary cesarean delivery in this subgroup were failure to progress (53.2%), nonreassuring FHR tracing (27.5%), and elective (7.6%).
Multiple gestation was the stated indication for a primary cesarean delivery in 1,187 women (3.1% of primary cesarean deliveries, involving 1,035 sets of twins and 152 higher-order multiples). In the 1,035 sets of twins for which multiple gestation was a cited indication for cesarean delivery, both fetuses were in the cephalic presentation in 263 cases (25.4%), twin A was cephalic and twin B was noncephalic in 255 cases (24.6%), twin A was noncephalic in 276 cases (26.7%), and presentation was not recorded in 241 cases (23.3%).
Among the 14,821 women (38.5%) who had a primary cesarean delivery after undergoing labor induction, the most common indication for cesarean delivery was failure to progress (59.3% of primiparous women and 40.4% of multiparous women), followed by nonreassuring FHR tracing (27.4% of primiparous women and 37.5% of multiparous women). Cervical examination information was available for 9,456 women who had a primary cesarean delivery after labor induction; 70.2% (69.9% of primiparous women and 71.9% of multiparous) had an unfavorable cervix (simplified Bishop score less than 5). The induction was elective for 10.4% of primiparous women and for 17.3% of multiparous women with an unfavorable cervix.
When grouped into hierarchical, mutually exclusive categories, 61.3% of all primary cesarean deliveries were considered clinically indicated (65.7% of primiparous women and 49.3% of multiparous women), 36.1% were mixed (31.6% of primiparous women and 48.2% of multiparous women), and 2.7% were truly elective (2.7% of primiparous women and 2.6% of multiparous women).
To identify opportunities to reduce the primary cesarean delivery rate and, in turn, to lower the total cesarean delivery rate, it is logical to scrutinize the most common indications for primary cesarean delivery. Of the three most common indications in our study, failure to progress, nonreassuring FHR tracing, and fetal malpresentation, failure to progress is of particular interest because it strongly affected the cohort of primiparous women at term with a singleton gestation in cephalic presentation. Of all primary cesarean deliveries in our study, 45.6% were performed in primiparous women at term with a singleton fetus in cephalic presentation, supporting previous findings that the cesarean delivery rate among primiparous women at term with a singleton gestation in cephalic presentation contributes substantially to the overall cesarean delivery rate.16,17
In a previous analysis of Consortium on Safe Labor data, Zhang et al18 concluded that 6 cm should be considered the start of the active phase of labor. In our cohort, 42.6% of primiparous women and 33.5% of multiparous women underwent a primary cesarean delivery for failure to progress when the cervix was dilated less than 6 cm. From this we deduce that waiting longer for labor to progress could have a major effect on decreasing the primary cesarean delivery rate.
Of women in our study with prolonged second stage diagnosed, 20.5% were delivered in less than 3 hours (for primiparous women) and in less than 2 hours (for multiparous women) from the time of complete dilation. Only 1.1% of these women were given a trial of operative vaginal delivery. This supports the idea that conservatively managing the second stage of labor, by allowing adequate time and encouraging operative vaginal delivery, when appropriate, also may have a major effect on decreasing the primary cesarean delivery rate.
The second most common indication for primary cesarean delivery in our study was nonreassuring FHR tracing. Finding opportunities to lower the primary cesarean delivery rate by targeting cesarean deliveries performed for this reason is difficult because interpretation of nonreassuring FHR tracing is highly subjective and strongly influenced by obstetric practice. Moreover, our data were collected before the introduction of the three-tiered interpretation of FHR tracing.19 Thus, a limitation of this study is that we were unable to quantify cesarean deliveries that were performed for nonreassuring FHR tracing but likely were avoidable.
The third most common indication for cesarean delivery in our cohort was fetal malpresentation. The American College of Obstetricians and Gynecologists advocates offering external cephalic version to patients with fetal malpresentation.20 Because attempted external cephalic versions were not captured in the Consortium on Safe Labor data, we could draw no conclusions about their effect on the primary cesarean delivery rate.
Turning to the less common indications for cesarean delivery, elective cesarean deliveries are an obvious target for reducing the primary cesarean delivery rate. Although the percentage of women who elected a primary cesarean delivery was relatively small, presumably many of these cesarean deliveries could have been avoided. In at least one-fourth of primary cesarean deliveries performed for women with twin gestations, both twins were in cephalic presentation. In another one-fourth, the presenting twin was in cephalic presentation. Some providers may have limited experience with the management of a noncephalic second twin during vaginal delivery; as a consequence, patients and providers may opt for a primary cesarean delivery to avoid cesarean delivery of the second twin after vaginal delivery of the first. A possible opportunity to reduce the primary cesarean delivery rate is to increase training in the delivery of the noncephalic second twin through the use of breech extraction or external cephalic version.
Recognizing that 38.5% of women in our cohort had a primary cesarean delivery after induction of labor, it is tempting to assert that avoiding labor induction could reduce the rate of primary cesarean delivery. However, our data neither support nor refute this claim. Further research is needed regarding the relationship between labor induction and primary cesarean delivery, with women undergoing induction being compared with those who are expectantly managed at a given gestational age, not compared with those in spontaneous labor.21
Among women in our cohort who had a cesarean delivery for suspected fetal macrosomia, 97.3% of neonates had a birth weight of less than 5,000 g. The American College of Obstetricians and Gynecologists does not recommend offering a cesarean delivery until the suspected fetal weight is more than 4,500 g in diabetic women and more than 5,000 g in nondiabetic women.22 Our findings highlight the well-described limitations of antenatal diagnosis of estimated fetal weight, both clinical and ultrasonographic.22
A strength of this study is inclusion of women from multiple institutions in nine states and the District of Columbia, thus providing a diverse population. Limitations included incomplete medical records and reliance on data entered into specified fields of electronic medical records. In addition, because more than one indication for cesarean delivery was given for 11.3% of women in our cohort, our ability to determine the primary indication was limited. A previous uterine scar was described in 4.2% of multiparous women and in 1.4% of primiparous women, and we were unable to determine the reason for the uterine scar. For primiparous women, it was assumed that the scars represented previous myomectomies, but the higher rate among multiparous women suggests that some primary cesarean deliveries actually may have been repeat cesarean deliveries that were recorded incorrectly.
To summarize, in this large cohort of women undergoing primary cesarean delivery, examination of indications as recorded in the medical record reveals potential targets to reduce the primary cesarean delivery rate and, in turn, lower the total cesarean delivery rate. Chief among these are decreasing the number of cesarean deliveries performed for failure to progress by using 6 cm as the cut-off for active labor when assessing failure to progress and conservatively managing the second stage of labor by allowing adequate time and encouraging operative vaginal delivery, when appropriate. These actions may be particularly important in the primiparous woman at term with a singleton fetus in cephalic presentation.
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