The influence of maternal body mass index on myometrial oxytocin receptor expression in pregnancy.

Obese pregnant women have higher rates of dysfunctional labor patterns, need for oxytocin augmentation, labor induction, postdates pregnancy, and cesarean delivery compared to normal weight pregnant women. We tested the hypothesis that myometrial oxytocin receptor (OXTR) gene and protein expression are affected by obesity in pregnancy. Myometrial samples were obtained at the time of cesarean delivery from the upper aspect of the uterine hysterotomy incision and processed for real-time quantitative polymerase chain reaction and Western blot. There were 63 myometrial samples available for analysis. The median body mass index (BMI) at delivery was 31.0 kg/m(2) (interquartile range, 26.0, 40.0 kg/m(2)), and the median gestational age at delivery was 38.0 weeks (interquartile range, 33.0, 39.1 weeks). The OXTR gene expression did not correlate with maternal BMI at delivery by linear regression, and the median OXTR gene expression did not differ between women with a BMI ≤ 30 kg/m(2) and those with a BMI ≥ 40 kg/m(2). The OXTR protein expression was also not affected by maternal BMI. Myometrial OXTR gene expression appears to be independent of BMI at the time of delivery. Dysfunctional labor patterns and increased oxytocin utilization seen in obese women may not be due to differences in OXTR expression, though functional studies are required.