COMPARATIVE-STUDIES ON THE INITIATION OF LABOR

Parturition is a multifactorial physiological process that involves mu ltiple interconnected positive feedforward and negative feedback loops . Each of these loops is connected to others in a carefully time-regul ated fashion. When parturition occurs normally. both fetal and materna l processes are involved. Recent reseal ch in pregnant sheep and nonhu man primates shows clearly that the fetus determines the duration of g estation and the mother determines the time of day at which labor begi ns. The fetal hypothalamo-pituitary-adrenal axis plays a fundamental r ole in stimulating increased estrogen production in late gestation. Es trogen then activates maternal circadian rhythms that increase oxytoci n secretion. As a result, uterine contraction patterns are switched fr om contractures to contractions. (C) 1998 Elsevier Science Ireland Ltd .