Some aspects of the metabolic and hormonal adaptation to pregnancy.

Metabolic adaptations to pregnancy are directed towards ensuring fetal growth and development, provision of a fetal store of energy, and the establishment of a maternal bank of energy. At any one time the demands of these objectives are competing for the available dietary energy, yet to ensure successful reproduction all three must be met. Current concepts suggest that the metabolic adaptation to pregnancy is designed primarily to safeguard against variable and restricted energy intake and that this is achieved by 1) a reduction in energy expenditure, resulting from decreased activity combined with increased metabolic efficiency, 2) phased metabolic activity affecting carbohydrate, fat and protein. Conservation of energy in maternal adipose tissue dominates the first half of pregnancy, while in late pregnancy the available energy is redirected to the fetus. This biphasic metabolism is programmed by the placental steroids whose secretion is independent of maternal diet. Internal redistribution of substrate under hormonal control is the main characteristic of the metabolic adaptation to pregnancy. The precise mechanisms underlying these adjustments have still to be defined.