Maternal adaptations to pregnancy and the role of the placenta

Delivery of an optimally grown, viable infant defines a successful pregnancy. Optimal growth is achieved by the interaction of maternal, placental, and fetal systems to deliver maternal nutrients to the placenta, transfer them to the fetus, and maximize their utilization for fetal growth. Pregnancy is characterized by profound changes in the maternal immune, metabolic, cardiovascular, and renal systems to ensure a successful pregnancy and adequate fetal growth. The fetal-placental unit secretes many hormonal signals, the roles of which include redirecting maternal physiology and metabolism to direct substrate toward the fetus and support normal fetal growth. The physiological adaptations of pregnancy begin shortly after conception, indeed before the establishment of a fetal-placental unit, and thus in their early phases must be directed by maternal signals, including those from the corpus luteum. Subsequently feto-placental signals play a major role in regulation of maternal metabolism. This chapter describes the maternal adaptation to pregnancy and the role of the placenta in nutrient transfer to the fetus. The changes in the cardiovascular system seen in pregnancy are by far the largest physiological challenge this system will face throughout the life cycle and include anatomical changes, increased blood volume and cardiac output, and a decrease in systemic vascular resistance. Ventricular wall muscle mass increases in the first trimester, followed by an increase in end-diastolic volume in the second and early third trimesters to increase cardiac compliance.