Effects of morphine administration on the fetal production of oxytocin in labour.

1. Animal and human work has indicated that maternal oxytocin secretion is under the control of endogenous opiates. Previous workers have described the fetal production of oxytocin in addition to maternal production. The study of the interaction between exogenously administered opiates and oxytocin secretion may give insight into the activity of any opiate-mediated regulatory mechanism of oxytocin secretion in the fetus. This study was designed to investigate the effect of an opiate (5 mg of morphine) given to the mother on the fetal production of oxytocin in labour. 2. Morphine was given by the attending clinicians for analgesic purposes to women in the first stage of labour. After delivery umbilical artery vein and maternal vein specimens were taken. 3. Four groups of patients were studied: women after normal vaginal delivery without analgesia in labour (n=10); women after normal vaginal delivery who had morphine administration in the first stage of labour (n=12); women who had an emergency Caesarean section in the first stage of labour (n=11); women who had an elective Caesarean section at term who were not in labour (n=11). 4. Oxytocin levels were measured by radioimmunoassay in the maternal vein, umbilical artery and umbilical vein specimens. Morphine was measured by radioimmunoassay in the umbilical vein specimens. 5. The umbilical artery minus vein concentration of oxytocin was calculated for each patient (A-V). There was no change in the umbilical (A-V) concentration of oxytocin if morphine had been given to the mother in labour; this applied to fetuses delivered vaginally or by Caesarean section. When the fetuses who were exposed to morphine were analysed separately, there was no correlation between the umbilical vein morphine concentration and the umbilical (A-V) oxytocin concentration either in Caesarean or vaginal deliveries. 6. Fetal oxytocin production was not affected by the maternal administration of morphine in the first stage of labour. This applies to the oxytocin production in the first and second stage of labour.