Dystocia correlates with body mass index in both spontaneous and induced nulliparous labors

To assess the influence of body mass index (BMI) on labor outcome in both induced and actively managed spontaneous nulliparous labors.

This is a prospective observational study of all consecutive nulliparous women who delivered in the National Maternity Hospital, Dublin in 2008. Labor outcome variables examined in relation to BMI included duration of labor, oxytocin requirements, epidural use, mode of delivery, and infant birthweight.

Of 4162 nulliparous women who labored during the study period, accurate BMI data were available on 3158, who constituted the study group. Of these women, 2143 (68%) were in spontaneous labor and 1015 (32%) had labor induced. A statistically significant association was found between maternal BMI at first antenatal visit and the need for intrapartum cesarean section (CS) in both spontaneous and induced labors (p < 0.05). A significantly poorer response to oxytocin augmentation was observed in women with a higher BMI, as indicated by an increased intrapartum CS rate for dystocia despite oxytocin augmentation. There was a linear relationship between maternal BMI and gestational age at onset of spontaneous labor.

Our results in a large consecutive series of nulliparous labors confirm the potent influence of increasing maternal BMI on intrapartum events.