Evidence of a foetal role in determining the length of gestation.

THIS paper reviews evidence that the foetus plays a vital role in determining gestation at labour. The hypothesis was not the keystone of our work initially, but evidence of foetal regulation of the myometrium became increasingly apparent during the course of studies on uterine contractility in human pregnancy. Work on induction of labour (Turnbull & Anderson, 1967, 1968a, b) made us aware of the great variation from patient to patient in the level of spontaneous uterine activity in late pregnancy. We also observed that uterine sensitivity to oxytocin was greater in cases delivered at term than in those with prolonged pregnancy. However, we did not know from this whether uterine sensitivity to oxytocin, probably in conjunction with spontaneous activity, declined with advancing gestation beyond term, or whether the uterus had been insensitive and inactive throughout pregnancy.