least 18 states have appropriated state funds to extend the reach of the WIC program (B. Jendrysik, Food and Nutrition Service, U.S. Department of Agriculture, personal communication, 1991).
During pregnancy, maternal requirements for all nutrients increase; this is reflected in higher Recommended Dietary Allowances (RDAs) 46 for most nutrients during pregnancy (see Table 2-1). For some nutrients, the evidence indicates a direct link between chronic maternal deficiencies and poor outcomes for the mother or the infant. For example, prolonged deficiency of iron, folate, or vitamin B12 (or any combination of these) may lead to anemia in the mother; deficiency of vitamin D may lead to neonatal hypocalcemia and to maternal osteomalacia; and deficiency of vitamin A may lead to restricted fetal growth.10 On the other hand, excessive intake of some nutrients may be harmful to the fetus, especially very early in pregnancy (see the previous section, "Preconceptional Nutrition").
In addition, total food intake (which serves as a proxy for energy intake) influences gestational weight gain. A large body of evidence indicates that gestational weight gain, particularly during the second and third trimesters, is an important determinant of fetal growth. Table 2-2 summarizes recommendations for total gestational weight gain. In a study of nearly 7,000 births, Parker and Abrams47 found that maternal weight gains within these recommended ranges were associated with better outcomes: fewer infants were either small for gestational age or large for gestational age, and fewer woman had cesarean deliveries.
A well-balanced diet is the appropriate source of nutrients during pregnancy. For the majority of pregnant women, iron is the only nutrient for which requirements cannot reasonably be met by diet alone. The 1990 IOM report Nutrition During Pregnancy10 recommends a daily supplement containing 30 mg of ferrous iron as a part of routine care during the second and third trimesters; the report also recommends that guidance be provided for the safe, effective use of this supplement. Routine determination of the hemoglobin value or hematocrit is advised to identify women who need higher iron intake.