Influence of Body Mass Index on Gestation and Delivery in Nulliparous Women: A Cohort Study

: To assess the influence of obesity on pregnancy and delivery in pregnant nulliparous women. Methods: A cohort, longitudinal, retrospective study was conducted in Spain with 710 women, of which 109 were obese (BMI > 30) and 601 were normoweight (BMI < 25). Consecutive nonrandom sampling. : maternal age, BMI, gestational age, fetal position, start of labor, dilation and expulsion times, type of delivery and newborn weight and height. Results: The dilation time in obese women (309.81 ± 150.42 min) was longer than that in normoweight women (281.18 ± 136.90 min) ( = 0.05, Student's -test). A higher fetal weight was more likely to lead to longer dilation time (OR = 0.43, 95% CI 0.010-0.075, < 0.001) and expulsion time (OR = 0.027, 95% CI 0.015-0.039, < 0.001). A higher maternal age was more likely to lead to a longer expulsion time (OR = 2.054, 95% CI 1.17-2.99, < 0.001). Obese women were more likely to have gestational diabetes [relative risk (RR) = 3.612, 95% CI 2.102-6.207, < 0.001], preeclampsia (RR = 5.514, 95% CI 1.128-26.96, = 0.05), induced birth (RR = 1.26, 95% CI 1.06-1.50, = 0.017) and cesarean section (RR = 2.16, 95% CI 1.11-4.20, = 0.022) than normoweight women. : Obesity is associated with increased complications during pregnancy, an increased incidence of a cesarean section and induced birth but it has no significant effect on the delivery time.