Menstrual cycle-related fluctuations in oxytocin concentrations: A systematic review and meta-analysis.

Oxytocin affects physiological and psychological functions that are often expressed sex-specifically, suggesting interactions between oxytocin and sex hormones. As female sex hormone concentrations change during the menstrual cycle, oxytocin might fluctuate, too. This systematic review and meta-analysis investigated endogenous oxytocin concentrations across menstrual cycle phases in healthy women. Data from 13 studies (120 women) showed a significant increase of oxytocin concentrations from the early follicular phase to ovulation (g = 0.39 [0.25; 0.53], p < .001) and a significant decrease from ovulation to the mid-luteal phase (g = -0.50 [-0.81; -0.18], p < .001). There were no significant differences between the early follicular and mid-luteal phase (g = -0.19 [-0.70; -0.32], p = .471). These findings contribute to a deeper understanding of differences in normal and abnormal psychobiological processes in women. They highlight the necessity to consider the menstrual cycle phase in studies on oxytocin in women.