The association of maternal weight with cesarean risk, labor duration, and cervical dilation rate during labor induction.

OBJECTIVE: To assess the relationship among maternal weight and cesarean delivery, cervical dilation rate, and labor duration.
METHODS: We used a secondary analysis of 509 term women who were previously enrolled in a prospective observational study of a labor induction protocol in which standardized criteria were used for labor management. A variety of analyses were performed, both unadjusted and adjusted. P <.05 was considered significant.
RESULTS: The mean +/- standard deviation weight of women who underwent a cesarean (97 +/- 29 kg) was significantly higher than that of women who were delivered vaginally (87 +/- 22 kg, P <.001). In a logistic regression model of nulliparas who comprised 71% of the study population, after adjustment for the confounding effects of infant birth weight, maternal age, initial cervical dilation, and diabetes, for each 10-kg increase in maternal weight, the odds ratio for cesarean delivery was significantly increased (odds ratio 1.17; 95% confidence interval 1.04, 1.28). In a linear regression model also limited to nulliparas and after adjusting for the same confounders, the rate of cervical dilation was inversely associated with maternal weight: for each 10-kg increment, the rate of dilation was decreased by 0.04 cm/h (P =.05). Similarly, labor duration was positively associated with maternal weight: for each 10-kg increment, an increase in the oxytocin to delivery interval of 0.3 hours was observed in nulliparas (P =.02). Neither lower rates of oxytocin administration to heavier women nor diminished uterine responsiveness (as reflected in measured Montevideo units) accounted for the slower labor progress.
CONCLUSION: In nulliparous women undergoing labor induction, maternal weight was associated with a higher cesarean risk and longer labor and was inversely proportional to the cervical dilation rate. LEVEL OF EVIDENCE: II-2