Primate parturition and the role of the maternal circadian system.

Several 24-h rhythms have been observed in the mother and in the fetus during primate gestation. In the mother, 24-h rhythms occur in biophysical variables, pregnancy-associated plasma hormones and preparturient myometrial activity. In addition, both pregnant non-human primates and pregnant women deliver preferentially during the night and early morning hours. A crucial question pertaining circadian rhythms is whether 24-h rhythms that may be observed during pregnancy are endogenous in nature and entrained by the light-dark cycle or whether the daily photoperiod is a causal stimulus. Our work has addressed the role of the maternal and fetal circadian system for 24-h rhythms in pregnancy-associated maternal plasma hormones, preparturient myometrial activity and parturition in human and non-human primate pregnancy. In the present review, the results of some of our studies are being discussed in combination with data available from the literature. It is apparent that 24-h rhythms that may be observed during primate pregnancy are determined by the maternal circadian system, suggesting that the developing fetus receives information about the ambient time of the day via the mother. Fetal entrainment by the mother may ensure fetal cooperation so that parturition occurs at the most favorable time of the day. We conclude that the functioning of the maternal circadian system is integral to the pregnant state. Thus, proper care and management of pregnant women and the ultimate outcome of obstetrics may benefit from more timely methodologies. A chronopharmacological attitude towards the prevention of premature labor and the induction and augmentation of labor at term may yield new therapeutic strategies. Such an approach will enable delivery to take place under optimal conditions for mother and child.