Oxytocin levels in low-risk primiparas following breast stimulation for spontaneous onset of labor: a quasi-experimental study

BACKGROUND: Breast stimulation is performed to self-induce labor. However, there are apparently no reports on hormonal evaluation during stimulation for consecutive days in relation to induction effect. We evaluated the salivary oxytocin level following 3 consecutive days of own breast stimulation for 1 h each day compared with no breast stimulation. METHODS: We used a quasi-experimental design. The participants were low-risk primiparas between 38 and 39 gestational weeks. Eight saliva samples per participant were collected at preintervention and 30, 60, and 75 min postintervention on the first and third days. The primary outcome was change in the salivary oxytocin level on the third day after 3 consecutive days of breast stimulation for 1 h each day compared with no breast stimulation. The secondary outcomes were the rate of spontaneous labor onset and negative events including uterine hyperstimulation and abnormal fetal heart rate. RESULTS: Between February and September 2016, 42 women were enrolled into the intervention group (n = 22) or control group (n = 20). As there were differences in the basal oxytocin levels between the 2 groups, to estimate the change in the oxytocin level from baseline, we used a linear mixed model with a first-order autoregressive (AR1) covariance structure. The dependent variable was change in the oxytocin level from baseline. The independent variables were gestational weeks on the first day of intervention, age, education, rs53576 and rs2254298, group, time point, and interaction of group and time. After Bonferroni correction, the estimated change in the mean oxytocin level at 30 min on the third day was significantly higher in the intervention group (M = 20.2 pg/mL, SE = 26.2) than in the control group (M = − 44.4 pg/mL, SE = 27.3; p = 0.018). There was no significant difference in the rate of spontaneous labor onset. Although there were no adverse events during delivery, uterine tachysystole occurred in 1 case during the intervention. CONCLUSIONS: The estimated change in the mean oxytocin level was significantly higher 30 min after breast stimulation on the third day. Thus, consecutive breast stimulation increased the salivary oxytocin level. Repeated stimulations likely increase the oxytocin level. TRIAL REGISTRATION: UMIN000020797 (University Hospital Medical Information Network; Prospective trial registered: January 29, 2016).