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Preterm delivery is the primary cause of neonatal mortality and morbidity worldwide. Labour at term occurs as a culmination of maturational events in both the fetus and maternal uterus. This process exhibits diurnal variation, with the onset of labour being more common at night. We have confirmed that this diurnal variation is present in gestations between 28 and 36 weeks, but is absent below 28 weeks. We hypothesise that this is because before 28 weeks of gestation, the onset of labour may result from a pathological rather than a physiological process. This may have important implications regarding any pharmacological approach to the prevention and/or treatment of very early preterm labour.

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.