Intrauterine Growth Restriction

After completing this article, readers should be able to: 1. List the most common identifiable cause of intrauterine growth restriction (IUGR). 2. List maternal conditions that can cause both IUGR and preterm delivery. 3. Characterize the effects of IUGR on fetal water, mineral, nitrogen, protein, glycogen, adipose tissue, total energy balance, and tissue mass. 4. Describe Doppler velocimetry findings suggestive of chronic fetal distress. 5. List potential adult disorders resulting from IUGR. Intrauterine growth restriction (IUGR) is defined as a rate of fetal growth that is less than normal for the growth potential of a specific infant. An enormous number and variety of established and possible causes have been identified. Potentially, any aberration of biological activity in the fetus can lead to growth failure. For example, deficiency or insufficient action of any one of the factors that influence fetal growth (see “Factors Influencing Fetal Growth” in this issue), alone or in combination, could lead to IUGR. The most common identifiable cause is fetal undernutrition due to placental insufficiency. Although most placentas that have insufficient function probably have specific deficits in nutrient transport capacity (eg, decreased placental vasculature with resulting decreased uterine and/or umbilical blood flow, decreased number or function of specific nutrient transporters), a smaller-than-normal placenta alone is sufficient to limit fetal nutrient supply. Small placental size can be natural, pathologic, or simply relative. For example, a small mother generally cannot produce a large placenta because her uterus is small. Similarly, even a normal-size mother can have a relatively small uterus, and, therefore, produce a small placenta if she carries more than one fetus. Experiments of artificially decreased placental growth have shown that any such restriction leads to fetal growth delay, confirming the direct relationship between placental and fetal size and the primary causal role of the placenta in determining fetal growth. However, there is …