Background
Obesity is a known risk factor for cesarean delivery. Limited data are available regarding the reasons for the increased rate of primary cesarean in obese women. It is important to identify the factors leading to an increased risk of cesarean to identify opportunities to reduce the primary cesarean rate.
Objective
We evaluated indications for primary cesarean across body mass index (kg/m 2 ) classes to identify the factors contributing to the increased rate of cesarean among obese women.
Study Design
In the Consortium of Safe Labor study from 2002 through 2008, we calculated indications for primary cesarean including failure to progress or cephalopelvic disproportion, nonreassuring fetal heart tracing, malpresentation, elective, hypertensive disease, multiple gestation, placenta previa or vasa previa, failed induction, HIV or active herpes simplex virus, history of uterine scar, fetal indication, placental abruption, chorioamnionitis, macrosomia, and failed operative delivery. For women with primary cesarean for failure to progress or cephalopelvic disproportion, dilation at the last recorded cervical examination was evaluated. Women were categorized according to body mass index on admission: normal weight (18.5-24.9), overweight (25.0-29.9), and obese classes I (30.0-34.9), II (35.0-39.9), and III (≥40). Cochran-Armitage trend test and χ 2 tests were performed.
Results
Of 66,502 nulliparous and 76,961 multiparous women in the study population, 19,431 nulliparous (29.2%) and 7329 multiparous (9.5%) women underwent primary cesarean. Regardless of parity, malpresentation, failure to progress or cephalopelvic disproportion, and nonreassuring fetal heart tracing were the common indications for primary cesarean. Regardless of parity, the rates of primary cesarean for failure to progress or cephalopelvic disproportion increased with increasing body mass index (normal weight, overweight, and classes I, II, and III obesity in nulliparous women: 33.2%, 41.6%, 46.4%, 47.4%, and 48.9% [ P < .01] and multiparous women: 14.5%, 20.3%, 22.8%, 27.2%, and 25.3% [ P < .01]), whereas the rates for malpresentation decreased (normal weight, overweight, and classes I, II, and III obesity in nulliparous women: 23.7%, 17.2%, 14.6%, 12.0%, and 9.1% [ P < .01] and multiparous women: 35.6%, 30.6%, 26.5%, 24.3%, and 22.9% [ P < .01]). Rates of primary cesarean for nonreassuring fetal heart tracing were not statistically different for nulliparous ( P > .05) or multiparous ( P > .05) women. Among nulliparous women who had a primary cesarean for failure to progress or cephalopelvic disproportion, rates of cesarean prior to active labor (6 cm) increased as body mass index increased, accounting for 39.3% of women with class I, 47.1% of women with class II, and 56.8% of women with class III obesity compared to 35.2% for normal-weight women ( P < .01).
Conclusion
Similar to normal-weight women, the indication of cesarean for failure to progress or cephalopelvic disproportion was the major factor contributing to the increase in primary cesarean in obese women, but was even more prevalent with increasing obesity class. The rates of intrapartum primary cesarean prior to achieving active labor increased with increasing obesity class in nulliparous women.
Introduction
Obesity is epidemic in the United States. In 2011 through 2012, 32% of women of reproductive age (20-39 years old) were obese (body mass index [BMI] ≥30 kg/m 2 ). Obese women have an increased risk of cesarean delivery even after adjusting for maternal comorbidities as well as a lower rate of vaginal birth after cesarean compared with normal-weight women. Although the rate of primary cesarean delivery declined from 22.1% in 2009 to 21.5% in 2012, the overall rate is still high. Limited data are available regarding the reasons for the increased rate of primary cesarean delivery in obese women. Small studies have demonstrated that failure to progress/cephalopelvic disproportion and nonreassuring fetal heart tracing (NRFHT) were the most common indications for primary cesarean delivery in obese women. In a retrospective study of 2251 obese women undergoing nonelective cesarean delivery, increasing BMI was associated with increased risks for cesarean delivery due to hypocontractility and NRFHT (defined by International Statistical Classification of Diseases, 10th Revision O62 and O68, respectively). However, in that study, failure to progress/cephalopelvic disproportion was not increased in obese women. It is important to identify the factors leading to an increased risk of cesarean delivery because obese women also have a higher risk of postoperative complications including endometritis, wound infection and separation, and venous thromboembolism. To identify opportunities to reduce the primary cesarean delivery rate, it is important to examine the contributors for increased risk of primary cesarean delivery in obese women who constitute one third of the US delivery population. Therefore, we investigated the factors contributing to the increased rate of cesarean delivery among obese women in a large US multicenter cohort study.
Materials and Methods
The Consortium on Safe Labor (CSL) was a retrospective cohort study of all women delivering at ≥23 weeks of gestation from 2002 through 2008 in 12 clinical centers with 19 hospitals across 9 American Congress of Obstetricians and Gynecologists (ACOG) US districts. All participating institutions obtained institutional review board approval.
The CSL included a total of 228,562 deliveries with 233,736 newborns delivered at ≥23 weeks of gestation after excluding 106 deliveries due to errors in identification. Data from the electronic medical record were abstracted and mapped to predefined classes at the data coordinating center. The data coordinating center performed data cleaning and logic checks. Sites validated 4 diagnoses including cesarean delivery for nonreassuring fetal heart rate tracing, neonatal asphyxia, neonatal intensive care unit admission due to a respiratory diagnosis, and shoulder dystocia. The variables were highly concordant with the medical records (>95% for 16 of 20 variables and ≥91.9% for all). We included singleton and multiple pregnancies in the present analysis. We excluded women with previous cesarean deliveries, fetus with a major congenital anomaly or chromosomal abnormality, antepartum stillbirth, and women with BMI unknown or <18.5 kg/m 2 . The final analysis was limited to 143,463 deliveries ( Supplementary Figure ).
We chose to use the maternal BMI on admission because this variable takes into account weight gain during pregnancy and was also recorded in labor and delivery on the majority of women. Information on maternal demographics and pregnancy outcomes was collected for evaluation based on maternal BMI at admission. Maternal BMI was categorized as normal weight for 18.5-24.9 kg/m 2 , overweight for 25.0-29.9 kg/m 2 , obese class I for 30.0-34.9 kg/m 2 , obese class II for 35.0-39.9 kg/m 2 , and obese class III for ≥40 kg/m 2 .
We compared percentages of indications for primary cesarean delivery across BMI classes. A sensitivity analysis was performed for the 3 most common indications stratified by gestational age category at delivery (23-32, 33-36, and ≥37 weeks of gestation). Indications were recorded in the medical record including failure to progress or cephalopelvic disproportion, NRFHT, malpresentation, elective, hypertensive disease, multiple gestation, placenta previa or vasa previa, failed induction, HIV or active herpes simplex virus, history of uterine scar, fetal indication, placental abruption, chorioamnionitis, macrosomia, and failed operative delivery. Percentages of each indication were calculated as the number of cesarean deliveries performed for each indication. The rates could add up to >100% if >1 indication was recorded.
Because some women had >1 indication and we could not identify which indication was the primary indication, we also grouped the indications for primary cesarean delivery into the following 3 hierarchical, mutually exclusive classes using criteria previously described by Zhang et al : clinically indicated; mixed; and truly elective. “Clinically indicated” was defined as nonreassuring fetal heart rate tracing, failure to progress, cephalopelvic disproportion, failed induction, failed trial of forceps or vacuum, placenta abruption, placenta previa, and history of shoulder dystocia. “Mixed” included indications where adequate information was not available such as previous uterine scar, malpresentation, fetal macrosomia, HIV infection, multiple gestation, preeclampsia/eclampsia, and other (ie, HIV infection without known viral load). Suspected macrosomia and multiple gestation are not absolute indications for primary cesarean delivery unless the estimated fetal weight is >4500 g for diabetic women, >5000 g for nondiabetic women, or noncephalic presentation in twins. Since estimated fetal weight or presentation of the twins were unknown in our study, we classified these as mixed indications. “Truly elective” was defined as cesarean for elective delivery as recorded in the medical record with no other indications recorded as well as nonmedically indicated reasons including 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. In cases in which >1 reason for cesarean delivery was given, and when there were reasons in >1 class, the delivery was placed in the higher ranking class in which clinically indicated outranked mixed, which, in turn outranked truly elective.
We further examined the timing of delivery relative to the first and second stage of labor. For this analysis, we excluded multiple gestation. For women with cesarean indication for failure to progress or cephalopelvic disproportion, dilation at the last recorded cervical examination was evaluated. For women with cesarean indication for arrest of decent, the time between full dilation and birth of the neonate was evaluated. Those women with unrecorded last cervical examination were excluded from this analysis.
Descriptive statistics were calculated for all study variables. The χ 2 test was used to compare maternal characteristics. Cochran-Armitage trend test was used to calculate the association between cesarean indications and BMI classes. All statistical analyses were performed using software (SAS 9.3; SAS Institute Inc, Cary, NC).
Materials and Methods
The Consortium on Safe Labor (CSL) was a retrospective cohort study of all women delivering at ≥23 weeks of gestation from 2002 through 2008 in 12 clinical centers with 19 hospitals across 9 American Congress of Obstetricians and Gynecologists (ACOG) US districts. All participating institutions obtained institutional review board approval.
The CSL included a total of 228,562 deliveries with 233,736 newborns delivered at ≥23 weeks of gestation after excluding 106 deliveries due to errors in identification. Data from the electronic medical record were abstracted and mapped to predefined classes at the data coordinating center. The data coordinating center performed data cleaning and logic checks. Sites validated 4 diagnoses including cesarean delivery for nonreassuring fetal heart rate tracing, neonatal asphyxia, neonatal intensive care unit admission due to a respiratory diagnosis, and shoulder dystocia. The variables were highly concordant with the medical records (>95% for 16 of 20 variables and ≥91.9% for all). We included singleton and multiple pregnancies in the present analysis. We excluded women with previous cesarean deliveries, fetus with a major congenital anomaly or chromosomal abnormality, antepartum stillbirth, and women with BMI unknown or <18.5 kg/m 2 . The final analysis was limited to 143,463 deliveries ( Supplementary Figure ).
We chose to use the maternal BMI on admission because this variable takes into account weight gain during pregnancy and was also recorded in labor and delivery on the majority of women. Information on maternal demographics and pregnancy outcomes was collected for evaluation based on maternal BMI at admission. Maternal BMI was categorized as normal weight for 18.5-24.9 kg/m 2 , overweight for 25.0-29.9 kg/m 2 , obese class I for 30.0-34.9 kg/m 2 , obese class II for 35.0-39.9 kg/m 2 , and obese class III for ≥40 kg/m 2 .
We compared percentages of indications for primary cesarean delivery across BMI classes. A sensitivity analysis was performed for the 3 most common indications stratified by gestational age category at delivery (23-32, 33-36, and ≥37 weeks of gestation). Indications were recorded in the medical record including failure to progress or cephalopelvic disproportion, NRFHT, malpresentation, elective, hypertensive disease, multiple gestation, placenta previa or vasa previa, failed induction, HIV or active herpes simplex virus, history of uterine scar, fetal indication, placental abruption, chorioamnionitis, macrosomia, and failed operative delivery. Percentages of each indication were calculated as the number of cesarean deliveries performed for each indication. The rates could add up to >100% if >1 indication was recorded.
Because some women had >1 indication and we could not identify which indication was the primary indication, we also grouped the indications for primary cesarean delivery into the following 3 hierarchical, mutually exclusive classes using criteria previously described by Zhang et al : clinically indicated; mixed; and truly elective. “Clinically indicated” was defined as nonreassuring fetal heart rate tracing, failure to progress, cephalopelvic disproportion, failed induction, failed trial of forceps or vacuum, placenta abruption, placenta previa, and history of shoulder dystocia. “Mixed” included indications where adequate information was not available such as previous uterine scar, malpresentation, fetal macrosomia, HIV infection, multiple gestation, preeclampsia/eclampsia, and other (ie, HIV infection without known viral load). Suspected macrosomia and multiple gestation are not absolute indications for primary cesarean delivery unless the estimated fetal weight is >4500 g for diabetic women, >5000 g for nondiabetic women, or noncephalic presentation in twins. Since estimated fetal weight or presentation of the twins were unknown in our study, we classified these as mixed indications. “Truly elective” was defined as cesarean for elective delivery as recorded in the medical record with no other indications recorded as well as nonmedically indicated reasons including 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. In cases in which >1 reason for cesarean delivery was given, and when there were reasons in >1 class, the delivery was placed in the higher ranking class in which clinically indicated outranked mixed, which, in turn outranked truly elective.
We further examined the timing of delivery relative to the first and second stage of labor. For this analysis, we excluded multiple gestation. For women with cesarean indication for failure to progress or cephalopelvic disproportion, dilation at the last recorded cervical examination was evaluated. For women with cesarean indication for arrest of decent, the time between full dilation and birth of the neonate was evaluated. Those women with unrecorded last cervical examination were excluded from this analysis.
Descriptive statistics were calculated for all study variables. The χ 2 test was used to compare maternal characteristics. Cochran-Armitage trend test was used to calculate the association between cesarean indications and BMI classes. All statistical analyses were performed using software (SAS 9.3; SAS Institute Inc, Cary, NC).
Results
Of 143,463 women, there were 21,929 (15.3%) normal-weight women, 55,997 (39.0%) overweight women, 38,007 (26.5%) obese class I women, 16,743 (11.7%) obese class II women, and 10,787 (7.5%) obese class III women ( Supplementary Figure ).
Demographic characteristics differed by BMI class ( Table 1 ). Obese women (classes I, II, and III) were more likely to be older, be multiparous, be non-Hispanic black, be smokers, have public insurance or self-pay, and have multiple gestations compared to normal-weight women. Obese women also were more likely to have chronic medical conditions and pregnancy complications including diabetes (pregestational and gestational) and hypertension (chronic hypertension, preeclampsia or syndrome of hemolysis, HELLP syndrome [elevated liver enzymes and low platelets], chronic hypertension with superimposed preeclampsia) compared to normal-weight women (all P < .01; data not shown). Obese women with chronic conditions delivered at a later gestational age and their neonates had a heavier birthweight on average ( P < .01). In addition, rates of fetal scalp electrode and intrauterine pressure catheter use were increased in obese women compared to normal-weight and overweight women ( P < .01). Oxytocin use increased with increasing BMI classes ( P < .01), whereas no clear trend was seen in epidural use. Obese women (classes I, II, and III) had lower rates of prelabor cesarean delivery and higher rates of labor induction compared with normal-weight and overweight women ( P < .01).
| Normal weight, n = 2712 | Overweight, n = 8659 | Obesity class I, n = 7603 | Obesity class II, n = 4222 | Obesity class III, n = 3564 | P value a | |
|---|---|---|---|---|---|---|
| Maternal age, y, mean (SD) | 27.6 (66.9) | 28.6 (6.8) | 28.2 (6.7) | 27.8 (6.5) | 27.3 (6.3) | <.01 |
| Nulliparous women, n (%) | 1993 (73.5) | 6529 (75.4) | 5482 (72.1) | 2965 (70.2) | 2462 (69.1) | <.01 |
| Race/ethnicity, n (%) | <.01 | |||||
| Non-Hispanic white | 1332 (49.1) | 4199 (48.5) | 3445 (45.3) | 1853 (43.9) | 1476 (41.4) | |
| Non-Hispanic black | 545 (20.1) | 1616 (18.7) | 1842 (24.2) | 1231 (29.2) | 1331 (37.4) | |
| Hispanic | 462 (17.0) | 1715 (19.8) | 1595 (21.0) | 828 (19.6) | 526 (14.8) | |
| Asian/Pacific Islander | 204 (7.5) | 585 (6.8) | 246 (3.2) | 69 (1.6) | 38 (1.1) | |
| Other, unknown | 169 (6.2) | 544 (6.3) | 475 (6.3) | 241 (5.7) | 193 (5.4) | |
| Health insurance, n (%) | <.01 | |||||
| Private | 1306 (48.2) | 4589 (53.0) | 3984 (52.4) | 2192 (51.9) | 1762 (49.4) | |
| Public or self-pay | 1084 (40.0) | 3087 (35.7) | 3021 (39.7) | 1804 (42.7) | 1655 (46.4) | |
| Other, unknown | 322 (11.9) | 983 (11.4) | 598 (7.9) | 226 (5.4) | 147 (4.1) | |
| Multiple gestation, n (%) | 120 (4.4) | 566 (6.5) | 529 (7.0) | 242 (5.7) | 188 (5.3) | <.01 |
| Smoking, n (%) | 199 (7.3) | 442 (5.1) | 444 (5.8) | 271 (6.4) | 299 (8.4) | <.01 |
| Gestational age at delivery, wk, mean (SD) | 37.3 (3.6) | 38.3 (2.8) | 38.4 (2.8) | 38.4 (2.7) | 38.3 (2.6) | <.01 |
| Gestational age category, n (%) | <.01 | |||||
| 23 0/7–27 6/7 | 101 (3.7) | 124 (1.4) | 101 (1.3) | 54 (1.3) | 39 (1.1) | |
| 28 0/7–32 6/7 | 194 (7.2) | 323 (3.7) | 298 (3.9) | 144 (3.4) | 112 (3.1) | |
| 33 0/7–36 6/7 | 460 (17.0) | 1079 (12.5) | 924 (12.2) | 512 (12.1) | 461 (12.9) | |
| 37 0/7–or greater | 1957 (72.2) | 7133 (82.4) | 6280 (82.6) | 3512 (83.2) | 2952 (82.8) | |
| Birthweight, g, mean (SD) | 2827.5 (774.2) | 3139.3 (695.5) | 3240.6 (735.4) | 3303.0 (753.2) | 3331.6 (756.1) | <.01 |
| Type of labor, n (%) | <.01 | |||||
| Prelabor cesarean delivery | 844 (31.1) | 2156 (24.9) | 1744 (22.9) | 847 (20.1) | 749 (21.0) | |
| Spontaneous labor | 1063 (39.2) | 3233 (37.3) | 2691 (35.4) | 1394 (33.0) | 1025 (28.8) | |
| Induction of labor | 805 (29.7) | 3270 (37.8) | 3168 (41.7) | 1981 (46.9) | 1790 (50.2) | |
| Fetal scalp electrode, n (%) | 506 (19.2) | 1897 (22.6) | 1763 (24.0) | 1149 (28.3) | 1092 (31.9) | <.01 |
| Intrauterine pressure catheter, n (%) | 579 (22.0) | 2355 (28.0) | 2295 (31.3) | 1370 (33.7) | 1203 (35.2) | <.01 |
| Oxytocin use, n (%) | 1173 (43.3) | 4509 (52.1) | 4333 (57.0) | 2518 (59.6) | 2196 (61.6) | <.01 |
| Epidural use, n (%) | 1732 (63.9) | 5999 (69.3) | 5190 (68.3) | 2885 (68.3) | 2333 (65.5) | <.01 |
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