Pregnancy Outcomes in Obese Women Better With Induced Labor

Norra MacReady

December 12, 2017

For obese pregnant women, elective induction of labor at 39 to 41 weeks of gestation may be a better choice than expectant management, the results of a study suggest.

Compared with expectant management, induced labor at 39 to 41 weeks of gestation was associated with a lower risk for cesarean delivery and severe maternal or neonatal morbidity, "with no change in the odds of infant and neonatal mortality," Cassandra M. Gibbs Pickens, PhD, from the Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, Georgia, and colleagues write. At 41 weeks, it was also associated with "reduced odds of some neonatal complications."

Maternal obesity, defined as a prepregnancy body mass index of 30 kg/m2 or more, has been associated with an increased risk for adverse maternal and neonatal outcomes, such as preeclampsia, shoulder dystocia, brachial plexus injury, and stillbirth, compared with findings in nonobese women. The researchers published their findings online December 4 in Obstetrics & Gynecology.

The incidence of all of these outcomes increases with advancing gestational age, so it is plausible that elective induction of labor and earlier delivery might prevent their occurrence. However, this possibility has not yet been adequately evaluated in obese pregnant women, so the authors conducted a retrospective cohort study to compare the risks and benefits of induced labor with those associated with expectant management in this patient population.

The researchers used data from the 2007 to 2011 California Linked Patient Discharge Data-Birth Cohort File, which includes information on more than 95% of childbirths to California residents. They included all obese women with singleton deliveries in cephalic presentation at 39 weeks of gestation or more, unless they had certain preexisting medical complications such as diabetes or hypertension, a prior cesarean delivery, or a neonate with a major congenital anomaly that would have affected clinical management.

For gestational weeks 39 to 41, the authors compared pregnancy outcomes among women who underwent induction without medical indication with those of women who underwent expectant management and delivered in a later week. The final analysis included 41,286 deliveries induced at weeks 39 to 41 and 122,301 deliveries managed expectantly.

Among nulliparous women induced at 39 weeks, 35.9% (95% confidence interval [CI], 34.1% - 37.8%) required cesarean delivery compared with 41.0% (95% CI, 40.4% - 41.6%) in the expectantly managed group. At 40 weeks, the rate of cesarean delivery among women who underwent induction was 41.8% (95% CI, 40.4% - 43.2%) compared with 46.2% (95% CI, 45.2% - 47.3%) among women managed expectantly (P < .05 for both comparisons). The difference at 41 weeks was not statistically significant. Similarly, the rates of cesarean delivery among parous women who underwent induced labor were lower at 39 and 40 weeks, but not 41 weeks, compared with women undergoing expectant management.

"In contrast," the authors write, "at 39 and 40 weeks of gestation, the risk of operative vaginal delivery was moderately increased among electively induced, as compared with expectantly managed, obese women (eg, among nulliparous women at 39 weeks of gestation, 8.9% [95% CI 7.9–10.1%] vs 7.1% [95% CI 6.8–7.4%], respectively." At 40 weeks, the rates of operative vaginal delivery were 7.8% and 6.8% among exposed and unexposed women, respectively (P < .05 for both comparisons). The differences at 41 weeks were not significant. Parous women showed a similar pattern.

Labor induction also was associated with a lower incidence of severe maternal morbidity, defined as a composite outcome consisting of postpartum hemorrhage, severe perineal lacerations, unplanned surgical procedure, uterine rupture, admission to an intensive care unit, maternal sepsis, and endometritis. At 39 weeks, the rate of severe maternal morbidity associated with elective induction among nulliparous women was 5.6% (95% CI, 4.9% - 6.3%) vs 7.6% (95% CI, 7.3% - 7.8%) associated with expectant management, and at 40 weeks, the rates were 6.8% and 8.5%, respectively (P < .05 for both comparisons). Here again, the pattern was similar among parous women.

Although rare, the frequency of neonatal and infant death was similar among exposed and unexposed women, regardless of parity. However, elective induction was associated with lower rates of admission to the neonatal intensive care unit. For example, at 39 weeks of gestation in nulliparous women, it was 7.9% (95% CI, 7.1% - 8.7%) vs 10.1% (95% CI, 9.8% - 10.4%) with expectant management (P < .05). Similar findings were seen at 40 weeks and among parous women.

Overall, in an analysis adjusted for maternal demographic characteristics, as well as first trimester initiation of prenatal care, birth year, and hospital type, labor induction was associated with reduced odds of cesarean delivery and severe maternal morbidity at 39 and 40 weeks among nulliparous and parous women. It was associated with a higher odds ratio of operative vaginal delivery among nulliparous women at 39 weeks, and among parous women at 40 weeks.

Among the neonates, elective induction was associated with a lower adjusted odds ratio of neonatal intensive care unit admission at 39 and 40 weeks of gestation, and with lower odds of most other neonatal complications.

Adjusted Odds Ratios of Maternal and Neonatal Outcomes Associated With Elective Labor Induction vs Expectant Management in Obese Pregnant Women (95% CI)

Outcome 39 Weeks of Gestation 40 Weeks of Gestation
Nulliparous Parous Nulliparous Parous
Cesarean delivery 0.82 (0.77 - 0.88) 0.79 (0.73 - 0.86) 0.85 (0.80 - 0.90) 0.81 (0.74 - 0.89)
Operative vaginal delivery 1.16 (1.03 - 1.31) 1.07 (0.97 - 1.20) 1.07 (0.95 - 1.20) 1.25 (1.10 - 1.41)
Severe maternal morbidity 0.75 (0.65 - 0.87) 0.83 (0.74 - 0.94) 0.84 (0.75 - 0.94) 0.75 (0.66 - 0.85)
Neonatal intensive care unit admission 0.79 (0.70 - 0.89) 0.75 (0.68 - 0.82) 0.84 (0.76 - 0.94) 0.77 (0.70 - 0.86)

Strengths of this study include the large, diverse sample size; the decision to compare the two groups at each week between 39 and 41 weeks; and the use of precise, robust statistical analyses. Limitations include the inability to evaluate stillbirths; possible bias involving cesarean delivery, which is associated with greater gestational age; and the possibility of residual confounding or underreporting of complications, the authors write. Also, "our results may only be generalizable to obese Californian women without pre-existing disease who delivered between 2007 and 2011."

Nevertheless, they conclude, "elective labor induction between 39 0/7 and 40 6/7 weeks of gestation may be associated with reduced maternal and neonatal morbidity among obese women and their offspring."

The authors have disclosed no relevant financial relationships.

Obstet Gynecol. 2018;131:12-22. Published online December 4, 2017. Abstract

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