Normal conception, embryonic development, and fetal development depend on the medical history, lifestyle, and nutritional state of the mother. While healthy babies can be born to women who are poorly fed, pregnancy and lactation often leave the mother with drained reserves and jeopardized health, and there is a greater probability of a high-risk birth.

According to the Food and Nutrition Board of the National Academy of Sciences, weight gain during pregnancy is now viewed as 25 to 35 lb. for women of average weight for height. A desirable weight gain should be worked out between the pregnant woman and her physician. The weight gain aids fetal growth and lowers the risks of low birth weights, infant mortality, and developmental problems. A large amount of new tissue is built and major changes occur in the mother’s body to accommodate growth and developmental problems. A large amount of new tissue is built and major changes occur in the mother’s body to accommodate growth and development of the placenta and fetus. Of the weight gained, one-third is converted to fetal tissue (6 to 8 lb.; the remainder forms the placeta (1 to 5 lb.), extra blood (3 to 4 lb.), enlarged breasts (1 to 2 lb.), enlarged uterus (2 lb.) and increased maternal fat stores (about 10 lb. [4.5 kg]). The weight gained during pregnancy is distributed among protein, fat, water, and blood.

Protein

The rate of protein synthesis remains high throughout embryonic and fetal development, although most of the fetal growth occurs in the last three months of pregnancy. Tissues like the brain, heart, and liver are composed mainly of protein (excluding water). New protein represents a net gain that is a positive nitrogen balance. There is an apparent correlation between maternal low blood protein levels and the risk of toxemia of pregnancy, which is associated with high blood pressure and protein loss in the urine.

Fat

A gain of nearly 10 lb. of body fat is equivalent to 47,500 calories. This provides an ample energy reserve for the mother and fetus and for lactation.

Water

Typically, about 60 percent of the gained weight is water. All new tissues require water because it is the principal constituent of the body and body fluids. Water is also stored as a fluid reserve to compensate for blood loss at childbirth. About 40 percent of pregnant women will retain excess water. The maternal blood volume increases by 30 percent, and the number of red blood cells increases by 18 percent. Maternal blood supplies the embryo and fetus with nutrients, including amino acids for protein synthesis and glucose and fatty acids for energy.

Nutritional Requirements

Protein

Dietary protein supplies amino acids, the raw materials for new protein. An estimated 1.3 g, 6.1 g, and 10.7 g of protein/day are required for the first, second, and third trimesters, respectively. Therefore, an additional 10 g/day above the adult requirement of 50 g/day throughout pregnancy is thought to meet the needs of most healthy pregnant women. The recommended dietary allowance (RDA) for protein during pregnancy is 60 g per day.

Calories

Metabolic changes occur that favor weight gain. Hormonal balance changes to maintain high blood glucose, amino acids, and fatty acids to store fat while slowing maternal utilization.

Calcium, Phosphorus, and Vitamin D

The RDA for calcium is 1,200 mg daily; the RDA for phosphorus is 1,200 mg and the RDA for vitamin D is 10 meg. The rate of calcium absorption jumps in the last two months of pregnancy to accommodate skeletal growth of the fetus; an infant at birth possesses nearly 30 g of calcium, mainly in bone. Dietary calcium may be better absorbed during pregnancy. However, it is important that the mother receive enough dietary calcium from conception until the end of lactation, and a calcium intake of 1,200 mg/day is advised. Although the amounts of phosphorus required for health are unknown, the total allowance should match that of calcium (1,200 mg/day). Vitamin D is required for calcium uptake and assimilation. Whether pregnancy increases the vitamin D requirement is not proven; however, the RDA for vitamin D is set at 10 meg/day for pregnant and lactating women. Early deposition of this fat-soluble vitamin provided in a balanced diet provides a reserve for later use when growth is very rapid.

Iron

Extra iron is required during pregnancy for increased production of red blood cells, to supply the fetus and placenta and to cope with blood loss during delivery. In the first trimester, cessation of menstruation compensates for additional needs of iron. To assure adequate iron throughout pregnancy, women need at 30 mg/day; this represents an additional 15 mg above the normal adult level. This high amount of iron cannot be supported by the usual American diet or by stored iron, so iron supplements are required. Because women do not menstruate during breast-feeding, iron requirements during lactation are essentially the same as those for nonpregnant women.

Folic Acid

Pregnancy increases the risk of deficiency when the intake of this fragile, water-soluble vitamin is marginal. The RDA for folic acid is 400 meg during pregnancy. To meet this requirement, vigilance is necessary in selecting foods. Evidence indicates that folic acid supplementation before conception and during the first months of pregnancy significantly reduces the risk of neural tube defects. (Federal agencies now recommend that women who are considering pregnancy as well as those who are pregnant consume 400 meg of folic acid daily.) During the first six months of lactation, the maternal RDA is 280 mg/day. The requirements for certain other nutrients also increase during pregnancy and breast-feeding (the following comparisons are made relative to the RDAs for nonpregnant adult women):

Vitamin A

Although the RDA does not increase during pregnancy, a 1.6-fold increase in the RDA during lactation is recommended (total of 1,300 meg of retinol).

Vitamin E

A 20 percent increase in the RDA during pregnancy, to 10 mg/day, is recommended. A 1.6-fold increase during the first six months of lactation, to 12 mg/day, is recommended.

Vitamin C

Pregnancy calls for a 17 percent increase in the RDA to 70 mg/day. The RDA during lactation is 95 mg/day.

Thiamin

A 50 percent increase in the RDA during pregnancy has been set at 1.5 mg/day. The RDA during lactation is about the same, 1.6 mg/day.

Riboflavin

There is a 23 percent increase during pregnancy to 1.6 mg/day. A 38 percent increase in riboflavin intake to 1.8 mg/day during lactation is recommended.

Niacin

Pregnancy entails a 13 percent increase in the RDA of niacin to 17 mg/day. A 23 percent increase during lactation to 20 mg/day is recommended.

Vitamin B₆

The RDA increases by 38 percent during pregnancy, to 2.2 mg per day. During lactation RDA increases to 2.6 mg per day.

Magnesium

The RDA increases to 300 mg daily during pregnancy. During lactation the RDA is 35 5 mg/day.

Zinc

The RDA increases by 25 percent during pregnancy to 15 mg per day. During lactation the requirement is 19 mg/day.

Iodine

The RDA increases by 17 percent to 175 meg daily. During lactation the RDA is 200 meg.

Selenium

The RDA increases by 18 percent to 65 meg/day. During lactation, the RDA is 75 meg.

Possible nutrition-related problems during pregnancy are:

• Anemia: Inadequate functional red blood cells are the end product of a chronic deficiency, most frequently of iron, though deficiencies of protein, copper, and vitamins like folic acid, vitamin B₆, vitamin E, vitamin C, or vitamin B₁₂ may cause anemia.

• Constipation: A decrease in muscle tone and the pressure of the growing fetus can cause constipation. Adequate water intake and fiber, in the form of vegetables, whole grains, and fresh fruit, are recommended.

• Diabetes: Certain hormones increase during pregnancy that counteract insulin, the hormone that lowers blood glucose, promoting glucose uptake by tissues. This can lead to gestational diabetes, which can cause placental malfunction, oversized infants, and labor complications.

• Excessive weight gain: There is no ideal body weight and weight does not indicate nutritional status. Too rapid weight gain can be caused by high-fat, high-calorie food that is low in important nutrients. Food choices need to be nutrient dense, that is, they need to contain a high percentage of vitamins, minerals, and fiber relative to calories. A major effort to lose weight during pregnancy can cause abnormal mental development in infants.

• Preeclampsia: This disorder affects about 7 percent of women in the third trimester of pregnancy. Water retention (edema), elevated blood pressure, and passage of protein in urine are signs of the more dangerous condition, toxemia, which threatens both the mother and fetus. Salt restriction and the use of diuretics can be hazardous and require medical supervision. The incidence of toxemia has declined with better prenatal care. High-quality protein is essential during pregnancy.

• Heartburn: stomach acid may be forced up into the esophagus by the enlarged fetus. Small, frequent meals may help avoid this problem. Pregnant women should avoid foods that cause digestive problems.

• Inadequate weight gain: Mothers whose nutritional deficiencies are corrected are more likely to have normal-term pregnancy and normal births.

• Drug and alcohol use; smoking: Studies of fetal alcohol syndrome suggest that there is no safe dose of alcohol during pregnancy. It has been suggested that alcohol may be one of the most common cause of birth defects and mental retardation in the United States. The use of cocaine, heroin, and addictive drugs during pregnancy leads to drug addicted infants who experience severe withdrawal symptoms at birth. Mental disturbances such as irritability and problems with social adjustment can continue throughout childhood and into adult life. Smoking is associated with reduced birth weight because carbon monoxide in cigarette smoke reduces the oxygen supply to the fetus. Many medications pass through the placenta and adversely affect the fetus. No medication or nutritional supplement should be taken during pregnancy without medical supervision.

Allen, Lindsay. “Anemia and Iron Deficiency: Effects on Pregnancy Outcome,” American Journal of Clinical Nutrition 71 (2000): 1,280S-1,284S.

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