Indications for primary cesarean delivery relative to body mass index

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.

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.

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.

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).

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.