Fetal cortisol and the initiation of labour in the human.

The role of the fetal adrenal activity in the initiation of parturition in the human has been investigated. Women were studied in the last trimester of pregnancy during treatment with betamethasone for prevention of the idiopathic respiratory distress syndrome. Although betamethasone caused a considerable drop in the cortisol concentrations of fetal plasma and amniotic fluid, the time to spontaneous delivery in this group was similar to that in matched controls. Moreover, cortisol in fetal scalp blood at the onset of parturition in untreated women did not differ between those with spontaneous and those with induced labour. Evidence is given that increase of circulating cortisol in the fetus during the course of parturition predominantly reflects a rise in maternal cortisol under the influence of labour. The strain of labour seems to partly override the betamethasone-induced inhibition of maternal cortisol release. The possible ability of the fetal adrenals to respond to stimuli is illustrated by comparison of cortisol concentrations in cord plasma after various forms of complicated deliveries.