Nutrient partitioning during adolescent pregnancy

Human adolescent mothers have an increased risk of delivering low birth wei ght and premature infants with high mortality rates within the first year o f life. Studies using a highly controlled adolescent sheep paradigm demonst rate that, in young growing females, the hierarchy of nutrient partitioning during pregnancy is altered to promote growth of the maternal body at the expense of the gradually evolving nutrient requirements of the gravid uteru s and mammary gland. Thus, overnourishing adolescent dams throughout pregna ncy results in a major restriction in placental mass, and leads to a signif icant decrease in birth weight relative to adolescent dams receiving a mode rate nutrient intake. High maternal intakes are also associated with increa sed rates of spontaneous abortion in late gestation and, for ewes deliverin g live young, with a reduction in the duration of gestation and in the qual ity and quantity of colostrum accumulated prenatally. As the adolescent dam s are of equivalent age at the time of conception, these studies indicate t hat nutritional status during pregnancy rather than biological immaturity p redisposes the rapidly growing adolescents to adverse pregnancy outcome. Nu trient partitioning between the maternal body and gravid uterus is putative ly orchestrated by a number of endocrine hormones and, in this review, the roles of both maternal and placental hormones in the regulation of placenta l and fetal growth in this intriguing adolescent paradigm are discussed. Im paired placental growth, particularly of the fetal component of the placent a, is the primary constraint to fetal growth during late gestation in the o vernourished dams and nutritional switch-over studies indicate that high nu trient intakes during the second two-thirds of pregnancy are most detriment al to pregnancy outcome. In addition, it may be possible to alter the nutri ent transport function of the growth-restricted placenta in that the imposi tion of a catabolic phase during the final third of pregnancy in previously rapidly growing dams results in a modest increase in lamb birth weight.