Journal Issue: Low Birth Weight Volume 5 Number 1 Spring 1995
Nutrition and Weight Gain
Concerns about nutrition during pregnancy fall into two basic areas, maternal weight gain and nutrient intake, both of which can potentially affect the health of the mother and infant. As with other lifestyle factors, a woman's nutrition and weight gain are closely linked to her socioeconomic status, cigarette smoking, and other health-related behaviors.
Maternal Weight Gain
Maternal weight gain during pregnancy results from a variety of factors, including maternal dietary intake, prepregnancy weight and height, length of gestation, and size of the fetus. The mother's prepregnancy weight and height are, in turn, a consequence of her genetic makeup, past nutritional status, and environmental factors. The relationship between a woman's caloric intake during pregnancy and her infant's birth weight is complex and is moderated through maternal weight gain and other mechanisms during pregnancy.13,14
Epidemiologic evidence has demonstrated a nearly linear association between maternal weight gain during pregnancy and birth weight,15,16 and an inverse relationship to the rate of low birth weight.16 It comes as no surprise that maternal weight gain during pregnancy is highly correlated with the birth weight of the infant because a large proportion of the weight gain is due to the growth of the fetus itself. Women with total weight gains of 22 pounds (10 kilograms) or less were two to three times more likely to have growth-retarded full-term babies than were women with a gain of more than 22 pounds. Once corrected for the duration of pregnancy, the relationship between weight gain and preterm delivery is uncertain.17,18
On average, women gain about 30 pounds during pregnancy. Teenage mothers, older mothers, unmarried mothers, and mothers with less than a high school education are most likely to have low or inadequate weight gain during pregnancy. Even after accounting for gestational age and socioeconomic status, African-American mothers gain less weight than white mothers (28 versus 31 pounds).19 It has been estimated that from 15% to 33% of women gain an inadequate amount of weight (less than 22 pounds) during pregnancy.13,19 Low weight gain may in part be the result of outdated medical advice and personal beliefs. In one study, one-quarter of the pregnant women believed that they should not gain more than 20 pounds during pregnancy.20 In addition, belief that a smaller baby is easier to deliver and thus that weight gain and fetal birth weight should be limited influences the amount of weight gained by some women.21
While higher maternal weight gain is linked with healthier fetal weight gains, women and clinicians are concerned that women may retain weight after delivery and be at greater risk for obesity. Recent studies have shown that weight retention following delivery increased as weight gain increased, and African-American women retained more weight than white women with comparable weight gains during pregnancy (7.2 versus 1.6 pounds).22 Thus, weight management programs would be appropriate for some women after delivery, but not during pregnancy.
Diet and Nutrient Intake
During pregnancy, the need for calories and nutrients, such as protein, iron, folate, and the other B vitamins, is increased to meet the demands of the fetus as well as the expansion of maternal tissues that support the fetus. As noted by Nathanielsz in this journal issue, the nutritional needs of the fetus are second only to the needs of the mother's brain. Thus, it is important for a pregnant woman to have a well-balanced, nutritious diet to meet the changing needs of her body and her fetus. Unfortunately, the direct relationship between specific vitamins and minerals and low birth weight is unclear, and controversy exists over the association between maternal hematocrit levels (which is a marker for anemia) and preterm birth.23-26
A pregnant woman's current nutritional status is determined by her prepregnant nutritional status, her current intake of nutrients, and her individual physiological nutrient requirements. Members of the National Academy of Sciences recently reviewed the available literature on dietary intake of nutrients and minerals among pregnant women. They found that the energy intake (calories) for U.S. women was consistently below recommended levels and that the amount of important vitamins and minerals in their diet was also substantially lower than the recommended daily allowance. On average, intakes of protein, riboflavin, vitamin B-12, niacin, and vitamin C exceeded the recommended daily allowance.27
Women at particular risk of nutritional inadequacy during pregnancy may require nutritional counseling. Groups at risk include women voluntarily restricting caloric intake or dieting; pregnant adolescents; women with low income or limited food budgets; women with eating patterns or practices that require balancing food choices, such as strict vegetarians; women with emotional illness; smokers; women with poor knowledge of nutrition due to lack of education or illiteracy; and women with special difficulties in food resource management because of limited physical abilities and poor cooking or budgeting skills.28