Abstract
Objective To investigate differences in oxytocin (OXT) biodistribution between nonobese and obese parturients during labor. Study Design Patients with body mass index (BMI) of either ≥ 18 ≤ 24.9 kg/m (2) ("nonobese") or ≥ 30 kg/m (2) ("obese") undergoing elective induction of labor were included ( N = 25 each). Blood samples were collected at baseline (T (0) ), and 20 minutes after maximal OXT augmentation or adequate uterine contractions (T (1) ) for OXT and oxytocinase assays. A mixed-model repeated-measures analysis of variance was used to test for group versus time interaction and analysis of covariance to detect a difference in OXT level at T (1) . Data presented as mean ± standard deviation or median (interquartile range), with p < 0.05 considered significant. Results The mean BMIs (kg/m (2) ) were 22.1 ± 1.6 and 35.9 ± 5.1 in the nonobese and obese groups, respectively. No differences were observed in either the duration of OXT infusion, total dose of OXT, or plasma OXT (pg/mL) either at T (0) or T (1) . However, plasma oxytocinase (ng/mL) was significantly lower at T (0) (1.41 [0.67, 3.51] vs. 0.40 [0.29, 1.12]; p = 0.03) in the obese group. Conclusion We provide preliminary evidence that the disposition of OXT may not be different between obese and nonobese women during labor.