Maternal physical activity, birth weight and perinatal mortality.

As a result of the acquisition of upright posture, adaptation to muscular exercise seems to be unique in man. It involves a redistribution of the cardiac output mediated by the sympathetic system towards priority organs which apparently do not include the pregnant uterus. This could explain the poor tolerance of the human fetus to maternal exercise. The hypothesis is supported by the independence of a detrimental effect of work from the effect of maternal nutrition and by an influence of maternal posture in late pregnancy on its outcome. Possible relations between maternal activity before and during late pregnancy and perinatal mortality are discussed in the context of this hypothesis.