Cumulative oxytocin dose during induction of labor according to maternal body mass index.

Objective: To determine the cumulative oxytocin dose needed to achieve vaginal delivery among obese and non-obese women.

Methods: A retrospective study was undertaken of women with singleton, term (≥37 weeks) pregnancies who delivered at an institution in California, USA, between May 1 and July 31, 2012. Women were deemed to be obese when their body mass index (BMI; calculated as weight in kilograms divided by the square of height in meters) was 30 or above. Cumulative oxytocin doses were calculated for women who achieved vaginal delivery.

Results: Overall, 413 women were included. Among 357 women for whom BMI data were available, 204 (57.1%) were obese. Vaginal delivery was achieved in 379 women. Among women who received augmentation after spontaneous labor onset, obese women trended towards more cumulative oxytocin (minimum: 24.7 ± 100.5 mU among women with a BMI of 18.50-24.99; maximum: 1580.5 ± 2530.5 mU among women with a BMI of 35.00-39.99; P=0.086). Women who underwent induction of labor required significantly more oxytocin with increasing BMI class (P<0.001), despite no difference in length of labor.

Conclusion: Obese women required a larger cumulative oxytocin dose to achieve vaginal birth during labor induction, but not during augmentation of labor. The physiology of spontaneous labor could supersede or influence the metabolic derangement facing obese patients undergoing induction of labor.