The effect of early labour, maternal analgesia and fetal acidosis on fetal plasma oxytocin concentrations

The role of arginine vasopressin in human labour: functional studies, fetal production and localisation of V1a receptor mRNA

OBJECTIVE

To investigate labour-associated changes in: 1. the myometrial contractile response to arginine vasopressin compared with oxytocin in vitro 2. fetal production of arginine vasopressin and 3. myometrial vasopressin V1a receptor mRNA.

DESIGN

The contractile response to vasopressin (compared with oxytocin) was investigated in paired myometrial strips in vitro. Blood was taken from the umbilical artery and vein at delivery and arginine vasopressin measured by radio-immunoassay. V1a receptor mRNA was determined by in situ hybridisation.

RESULTS

Myometrium was more sensitive to arginine vasopressin than oxytocin (P<0.05 for frequency, amplitude and activity integral in paired strips) after, but not before labour. There was a marked umbilical arteriovenous difference in arginine vasopressin concentration at delivery suggesting fetal production which was not influenced by labour. Myometrial vasopressin V1a receptor mRNA was not increased after the onset of labour.

CONCLUSIONS

The human uterus is extremely sensitive to arginine vasopressin in vitro. Arginine vasopressin is produced by the fetus but fetal formation is not increased during labour.

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.

The changing pattern of cerebral palsy in Avon

The overall rate of cerebral palsy excluding post-neonatal cases, has remained relatively constant, varying between 1.93 and 2.27 per 1000 births over the 20-year period between 1969 and 1988 in Avon. The rate of the subgroup of spastic cerebral palsy varied from 1.40 to 1.78 per 1000 births over the same time period. In singletons the corresponding figures were 1.80-2.17 per 1000 births and 1.28-1.67 per 1000 births, and in multiple births the figures were 7.12-8.80 per 1000 births and 7.12-8.44 per 1000 births. Although the overall rates have remained fairly constant there was an increase in incidence in the later years among children with low birthweight and short gestation.