The effect of labour and maternal oxytocin infusion on fetal plasma oxytocin concentration.

It is not known whether human labour is associated with increased fetal oxytocin production or transfer of oxytocin across the placenta. Previous reports are contradictory, due in part, to the influence of maternal analgesia on fetal production. We determined plasma oxytocin concentration in the umbilical artery and vein of women after vaginal delivery and after caesarean section with general anaesthesia before or after the onset of labour. The results demonstrate that fetal production of oxytocin is not influenced by general anaesthesia, thus enabling comparison of labour and nonlabour samples at caesarean section. Labour was not associated with an increase in fetal oxytocin production. Oxytocin was also measured in the umbilical artery and vein during maternal oxytocin infusion to assess placental transfer. The results do not support transfer of oxytocin across the placenta in women.