Regulation of Pregnancy, Parturition, and Lactation

Abstract

It is during our intrauterine development that many of the traits and characteristics that will affect our postnatal performance are established. At the time of fertilization, our genotype is established, but during fetal life, our further growth and development are influenced by many factors, including fetal genotype, placental function, local growth factors, circulating hormones, and the maternal environment. In North America, growth retardation leading to babies that are small for gestational age occurs in about 6% of all pregnancies. Preterm delivery occurs in 8–10% of all deliveries. Birth too soon of an infant that is very immature may be associated with conditions, such as cerebral palsy, and with respiratory distress syndrome in the newborn. In the US, the cost of preterm delivery—reflected in the cost of caring for these babies in Neonatal Intensive Care Units (NICUs)—has been estimated at $5–6 billion annually. The emotional cost for parents and families is substantial. Babies born too small may have additional longer-term problems. Recently, David Barker and colleagues have demonstrated that weight at birth is a powerful indicator of predisposition to disease in adult life (see Barker, 1994). The infant who is born inappropriately small has a much higher risk of developing high blood pressure, Type II diabetes, and of dying from cardiovascular disease in adult life. This relationship is particularly strong if the fetal growth reduction is asymmetrical and the placenta is disproportionately large. These relationships—small birthweight and subsequent hyper tension—can be reproduced in the offspring of rats fed low-protein diets or treated with glucocorticoids during pregnancy. Thus, understanding factors regulating pregnancy and pregnancy outcome as well as fetal growth and development are crucial for understanding, and potentially treating and preventing, diseases that may continue to affect us lifelong.