The fetal hypothalamus and pituitary in the initiation of labour.

Evidence is presented for a number of events in the fetal hypothalamic-pituitary axis which may play a key role in the onset of labour: (1) In the sheep fetus a progressive rise in the fetal circulating concentrations of corticotropin in the days preceding delivery; (2) In the human fetus a switch from the production of corticotropin-like fragments (melanotropin and corticotropin-like intermediate lobe peptide) to authentic corticotropin in the last weeks of gestation; there is evidence also for a placental origin of corticotropin; (3) In the human fetus, a release of oxytocin and vasopressin associated with the process of spontaneous labour.