In 2009, approximately 20.5% of reproductive-aged women in the United States were obese as defined by a body mass index (BMI, calculated as weight (kg)/[height (m)]2) of 30 or greater.1 Although the increased risks of maternal and fetal complications associated with obesity are well documented,2–82–82–82–82–82–82–8 less is known regarding the optimal delivery approach among obese women.
Because of the decreased likelihood of achieving vaginal delivery and potential concerns with intrapartum fetal monitoring, performing an emergent cesarean delivery, and increased risks of macrosomia and labor dystocia, some practitioners consider performing a cesarean delivery in the absence of labor for obese women. However, cesarean delivery in obese women is associated with higher rates of operative and postoperative complications such as excessive blood loss, operative time greater than 2 hours, wound infections, endometritis, and anesthetic challenges.9–119–119–11
Data are lacking on whether attempting vaginal delivery is associated with fewer adverse maternal and neonatal outcomes compared with a planned cesarean delivery. Many studies have investigated actual rather than intended delivery approach. The objective of our study was to compare maternal and neonatal outcomes in obese women by attempted delivery approach.
MATERIALS AND METHODS
The present study utilized data from the Consortium of Safe Labor, a retrospective cohort study by the Eunice Kennedy Shriver National Institute of Child Health and Human Development. The original study was designed in part to assess factors related to cesarean delivery in a modern obstetric cohort. Data on women delivering at one of 12 clinical centers and 19 hospitals were extracted from electronic medical records. A total of 228,562 deliveries occurred from 2002 to 2008.12 Institutional review board approval was obtained by all participating institutions and received exempt status for the current analysis given the deidentified data present for analysis.
Women were eligible for this analysis if they had BMIs of 30 or greater at delivery, no contraindication to labor, a singleton fetus in a vertex presentation, and a gestational age at delivery of 37 weeks or greater. Exclusion criteria included previous cesarean delivery (n=14,468), major congenital fetal malformations (n=8,216), or antepartum stillbirth (n=317), leaving 47,372 women for analysis (Fig. 1). For women with more than one pregnancy in the database, the analysis was limited to their first pregnancy recorded in the database.
Women were classified as attempting vaginal delivery if they had at least two vaginal examinations in the labor progression database.13 Women were classified as undergoing planned cesarean delivery if they were less than 6 cm dilated on admission to the labor ward and if the electronic medical record did not include a diagnosis of induction or augmentation of labor, intrapartum tocolysis, shoulder dystocia, vaginal lacerations, episiotomy, a cesarean delivery indication for failure to progress or failed induction, full cervical dilation, or onset of spontaneous labor noted at admission. Variable definitions were abstracted from the medical record and supplemented with International Classification of Diseases, 9th Revision codes where applicable. Gestational age was assigned according to the best obstetric estimate as recorded in the medical record.
Outcomes were composite and individual maternal and neonatal morbidities. The maternal composite outcome included intensive care unit admission, death, hemorrhage, blood transfusion, or thromboembolism. Additional outcomes assessed included hysterectomy, chorioamnionitis, endometritis, and postpartum fever. The neonatal composite outcome included neonatal intensive care unit (NICU) admission, neonatal death, seizure, ventilator use, birth injury defined as mechanical trauma incurred by the neonate during labor and delivery, or neonatal asphyxia. Additional outcomes assessed included Apgar score less than 7 at 5 minutes, shoulder dystocia, need for continuous positive airway pressure resuscitation or greater, and transient tachypnea of the newborn. Not all sites captured the outcome of interest in the electronic medical record; therefore, the composite and individual outcome analyses were limited to sites reporting data on the particular outcome.
Maternal and neonatal demographics were compared by attempted delivery approach for nulliparous and parous women using χ2 tests. Parametric data were analyzed with Student's t tests and Fisher's exact test. Wilcoxon two-sample test was applied for nonparametric data. To examine the optimal delivery approach among obese women, adjusted relative risks (RRs) and 95% confidence intervals (CIs) for maternal and neonatal morbidities were calculated using Poisson regression with a robust variance estimator for attempted vaginal compared with planned cesarean delivery (referent group) controlling for maternal age, gestational age, race, parity, marital status, cervical dilation at admission, hospital type, type of anesthesia, insurance status, drug, tobacco, or alcohol use, indication for delivery, and medical comorbidities (asthma, pre-existing and pregnancy-related hypertensive disorders, pre-existing and gestational diabetes).14
Body mass index at admission for delivery was analyzed as recorded in the medical record and stratified according to the World Health Organization's obesity classifications.15 Class I obesity was defined as BMI between 30.0 and 34.9, class II obesity 35.0–39.9, and class III obesity 40.0 or greater. Our primary analysis included all obese women (BMI 30 or greater) stratified by parity (nulliparous or parous). No correction was made for multiple comparisons. A P value of <.05 was considered significant. We conducted supplemental analyses by obesity class. Statistical analyses were performed using SAS 9.2.
Of the 47,372 singleton deliveries 37 weeks of gestation or greater eligible for a vaginal delivery, 46,047 (97.2%) women attempted vaginal delivery and 1,325 (2.8%) women had a planned cesarean delivery. In general, women who attempted vaginal delivery were younger, more likely to have private insurance, less likely to identify as non-Hispanic black, to have diabetes, or deliver at a university-affiliated teaching institution compared with women with a planned cesarean delivery (Table 1). Neonates of women attempting vaginal delivery compared with planned cesarean delivery weighed 204 g less for nulliparous and 186 g less for parous women (P=.01).
Among nulliparous women attempting vaginal delivery (n=15,268), the success rate was 72.6% and among parous women (n=23,426), it was 93.7% (Fig. 2). The rates of labor induction among nulliparous women (n=10,709) was 50.9% and 46.6% among parous women (n=11,662). Overall cesarean delivery rates were similar when comparing induction of labor and spontaneous labor with a slightly higher cesarean delivery rate noted with induction of labor in nulliparous women (Fig. 2).
For the analysis of nulliparous women with BMIs of 30 or greater, the maternal composite occurred more frequently among women attempting vaginal delivery (7.7% compared with 4.2% [adjusted RR 1.58, 95% CI 0.96–2.59]); however, this difference was not statistically significant (Table 2). Nulliparous women attempting vaginal delivery had a higher risk of postpartum hemorrhage, blood transfusion, and chorioamnionitis with fewer thromboembolic events compared with women undergoing a planned cesarean delivery (Table 2).
For parous women with BMIs of 30 or greater, the maternal composite occurred more often among women attempting vaginal delivery compared with planned cesarean delivery (7.6% compared with 2.5% [adjusted RR 2.45, 95% CI 1.23–4.90]) (Table 2). Women who attempted vaginal delivery had higher rates of blood transfusion but lower rates of postpartum fever and hysterectomy compared with planned cesarean delivery.
There was no difference in the neonatal composite outcome among nulliparous women attempting vaginal delivery. In the analysis of individual outcomes for attempted vaginal delivery compared with planned cesarean delivery, three neonatal outcomes were statistically different between the two groups. Compared with planned cesarean delivery, nulliparous women attempting vaginal delivery demonstrated a fivefold increase in birth injury with a 30% reduction in NICU admission and a 50% reduction in transient tachypnea of the newborn (Table 3).
In parous women, the neonatal composite outcome was decreased in women attempting vaginal delivery (6.0% compared with 11.6% [adjusted RR 0.65, 95% CI 0.51–0.83]). Increased rates of birth injury were noted among obese parous women attempting vaginal delivery. However, there were reduced rates of neonatal asphyxia, ventilator use, NICU admission, transient tachypnea of the newborn, and Apgar score less than 7 at 5-minutes parous (Table 3). Analyses by obesity subclass are presented in tabular form in Appendices 1 and 2, available online at http://links.lww.com/AOG/A699.
In a large U.S. multicenter cohort study of obese women, we aimed to compare maternal and neonatal outcomes in obese women by the attempted route of delivery. With regard to maternal morbidity in obese nulliparous women, attempting vaginal delivery was associated with increased rates of blood transfusion, hemorrhage, and chorioamnionitis but decreased rates of thromboembolism. In parous women, attempted vaginal delivery was associated with increased risks of composite maternal morbidity, blood transfusion, and chorioamnionitis with decreased risks of postpartum fever and hysterectomy. With respect to neonatal outcomes, birth injury was increased in nulliparous and parous women attempting vaginal delivery. Attempted vaginal delivery was also associated with decreases in NICU admission and transient tachypnea of the newborn in nulliparous women and decreased rates of the neonatal composite, neonatal asphyxia, transient tachypnea of the newborn, NICU admission, ventilation use, and Apgar score less than 7 at 5 minutes in parous women.
Previous studies have suggested that obese women have higher cesarean delivery rates as compared with their normal-weight counterparts.16,1716,17 Our study did not compare success rates with patients of normal BMI. We found the majority of obese women attempting vaginal delivery were successful, especially if they had previously delivered vaginally. Utilizing the Consortium of Safe Labor allowed analysis of less frequent outcomes in a large, contemporary, racially, and ethnically diverse cohort of U.S. women; however, there are limitations worth noting. Our study is retrospective in design, thus limiting our ability to discern why the health care provider selected a particular delivery route including whether the intended delivery route was influenced by other factors associated with obesity itself. The manner in which attempted delivery route was defined could have resulted in misclassification of the intended delivery approach. For example, it is possible that if a patient initially scheduled for a planned cesarean delivery presented in labor as previously defined, the patient would have been considered to have a vaginal delivery attempt. However, we only included women with at least two cervical examinations in the labor progression database as attempting a trial of labor to minimize this misclassification. Although this type of error is a limitation of the Consortium on Safe Labor, we feel that this classification would more accurately reflect the risks of a cesarean delivery in the absence of labor. However, given the large number of variables available in this database, including detailed information on labor as well as indications for cesarean delivery, this misclassification likely was small. Despite the utilization of a large, contemporary database to perform analysis on maternal and neonatal outcomes, the rarity of various outcomes (eg, maternal and neonatal death) limits the power to detect small differences between groups. Lastly, as a result of multiple comparisons, it is possible that some of the significant results occurred by chance.
When discussing route of delivery, the health care provider and patient should consider the clinical implications of an emergent cesarean delivery in the setting of morbid obesity. Although a vaginal delivery attempt was highly successful among obese women, the potential for increased complications such as failed intubation, bladder injury, hemorrhage, and increased incision to delivery time should be taken into account when selecting a delivery approach.9,18,199,18,199,18,19
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