Nutritional influences during pregnancy.

Maternal nutrition represents one of the important influences on the course and outcome of pregnancy and attention to nutritional factors (i.e., assessment of nutritional status, dietary advice, and follow-up evaluation) properly constitute an essential component of prenatal care. Nearly all nutrients are required in increased amounts during gestation but the magnitude of the increase varies from nutrient to nutrient. Caloric needs increase by 300 kcal per day, representing an addition of 15 per cent, and should be sufficient to support a weight gain averaging 350 to 400 gm per week during the last two trimesters. Total protein intake during pregnancy should be 1.3 gm per kg for the mature woman and somewhat higher for the adolescent. Gestational needs for iron cannot be met by diet and supplementation (in the form of simple ferrous salts, 30 to 60 mg daily) should be provided. Folate requirements are doubled during pregnancy and, while these can be met by diet, supplementation may be considered as an option. Provision of the gestational calcium allowance from food sources is readily possible if (and only if) daily products are consumed. The generally increased need for other nutrients can be provided readily by the properly selected diet. Thus, with respect to supplements, iron and perhaps folate should be advised routinely while other vitamin-mineral supplements are probably neither helpful nor harmful. Prescription of vitamin-mineral supplements cannot be expected to compensate for poor dietary habits. Dietary restriction of nutrients in general, and energy and sodium in particular, has the potential for impairing the maternal capacity to make the required physiologic adjustments of pregnancy and interfering with fetal development. Restriction of any nutrient to levels below the guidelines provided by the Recommended Dietary Allowances is rarely if ever advisable.