Nipple stimulation results in adequate contractions at lower plasma oxytocin concentration compared with IV oxytocin

Abstract

Nipple stimulation (STIM) has been suggested as a physiologic approach to labor induction. We sought to compare changes in plasma oxytocin concentration in patients undergoing labor induction via intravenous (IV) oxytocin versus STIM. This is a nested sub-study of an ongoing single center RCT. In the main RCT, nulliparas with singleton gestations ≥36 weeks planned to be induced with IV oxytocin are randomized to receive IV oxytocin infusion or to undergo STIM therapy via electric breast pump for ≥2 hours. For this sub-study, patients provided separate informed consent to provide plasma specimens at baseline, 2 hours, and at the time of adequate contractions (i.e. every 3 minutes). Blood specimens were centrifuged within 4 hours, and plasma frozen at -80°C. Oxytocin concentration was measured using enzyme linked immunosorbent assay. Statistical analyses were performed using GraphPad Prism. Samples were collected from 20 patients, 10 per treatment group. Baseline characteristics were similar between the two groups. There was wide variation in oxytocin concentration among participants. Patients randomized to receive IV oxytocin had significantly higher mean oxytocin concentrations at all time points compared to those in the STIM group. At 2 hours of treatment, when most women experienced ≥3 contractions in the preceding 10 minutes in both groups, there is a non-significant higher fold change in median oxytocin with IV oxytocin compared to STIM. At the time of adequate contractions, there was higher fold change in mean oxytocin concentration compared to baseline in the IV oxytocin group compared to STIM, despite most STIM patients having crossed over to IV oxytocin (IV Oxytocin mean 1.3, STIM mean 1.0; p < 0.04). These findings demonstrate that absolute circulating oxytocin concentration does not determine contraction frequency. Our findings suggest that STIM induces additional changes in maternal physiology that work synergistically with IV oxytocin.View Large Image Figure ViewerDownload Hi-res image Download (PPT)