Human parturition

The roles of fetal adrenal hormones, of maternal oestrogen and progesterone concentrations, and of uterine prostaglandin synthesis are considered in relation to the onset of human labour. Evidence that the fetal adrenal may be involved in the onset of labour is discussed with particular reference to both cortisol and dehydroepiandrosterone sulphate. Towards the end of pregnancy circulating concentrations of both unconjugated and conjugated oestrogens increase, and evidence for the presence of arylsulphatase (EC 3.1.6.1) in various intrauterine tissues suggests that the conjugates are potentially active. The rise in oestrogens and a concomitant drop in progesterone during the last few weeks of pregnancy may play a facilitatory role in the onset of labour. The changes in steroid concentrations are considered in relation to the promotion of prostaglandin synthesis leading to labour. Concentrations of prostaglandins in amniotic fluid show only minor changes before the onset of labour compared to those found with the onset of and during labour. Evidence for a local control of prostaglandin synthesis within the uterus is presented.