Effect of obesity on labor duration among nulliparous women with epidural analgesia.

Objective: The aim of this study was to describe the effect of obesity on the duration of labor, specifically latent and active phases of labor, and on mode of delivery, among nulliparous women with epidural analgesia.Study design: We conducted a retrospective cohort study, comparing a sample of nulliparous obese women (body mass index ≥30 kg/m2, n = 121) with a random sample of normal weight nulliparous (18.5 kg/m2 ≤body mass index ≤25 kg/m2, n = 161). Analysis included all obese women delivered at the Department of Obstetrics and Gynecology of Centro Hospitalar, São João, Porto, Portugal between 1 January and 31 December, 2016. Only women submitted to epidural analgesia were included. Information on maternal age, obstetric history, current pregnancy and labor characteristics (gestational age, birthweight, mode of delivery, total duration of labor, latent and active phases duration) was retrieved from electronic obstetrical databases and labor charts.Results: In our department, the prevalence of maternal obesity was 12.0%. Obese women had a significantly higher rate of cesarean delivery (47.1 versus 27.3%), fewer normal vaginal deliveries (28.9 versus 32.9%) and fewer instrumental vaginal deliveries (24.0 versus 39.8%). Labor induction was significantly more frequent among obese women (51.2 versus 29.2%; p = 0.001). The median (interquartile range) for length of latent phase when labor was induced with prostaglandins in the obese group was 23.3 hours (20.9). This was significantly longer than in normal weight women -15.6 hours (13.15) (p = 0.001). However, there was no significant difference in latent phase duration when labor was induced with oxytocin (12.4 versus 9.4 hours; p = 0.150). The medians (interquartile range) for length of latent phase in spontaneous delivery -6.5 hours (6.8) versus 6.6 hours (6.5) did not differ (p = 0.992). The duration of active phase was not significantly different between obese and normal weight (5.1 versus 5.1 hours; p = 0.784). For spontaneous labor, there was no difference between the two groups in the total duration of labor (11.9 versus 11.3 hours; p = 0.573). But for induced labor, the total duration was significantly higher among obese women (31.1 versus 21.4 hours; p = 0.001).Conclusion: Latent phase was longer in obese than normal weight women undergoing labor induction with prostaglandins. Obesity had no effect on duration of active phase. Obese women undergoing labor induction had a longer total duration of labor, compared to normal weight women mainly due to prolonged latent phase.