Nutrition during the preconception period, as well as throughout a pregnancy, has a major impact on pregnancy outcome. Among prepregnancy considerations, the prepregnancy Body Mass Index (BMI), folic acid status, and socioeconomic status are the most important.
Prepregnancy BMI is an important factor in predicting pregnancy outcome, since both low prepregnancy and high prepregnancy BMI are associated with an increased risk for a negative pregnancy outcome.
Folic acid, a B vitamin, has been shown to prevent birth defects of the brain and spinal cord known as neural tube defects (NTDs). The most common NTDs are spina bifida and anencephaly. Folic acid is therefore needed
RECOMMENDED TOTAL WEIGHT-GAIN RANGES FOR PREGNANT WOMEN BY PREPREGNANCY BODY MASS INDEX (BMI)
|Weight-for-height category||Recommended total weight gain|
|Young adolescents and black women should strive for gains at the upper end of the recommended range. Short women (157 cm, or 62 inches) should strive for gains at the lower end of the range. The recommended target weight gain for obese women (BMI 29.0) is at least 6.8 kg (15 lb).|
|BMI is calculated using metric units.|
|SOURCE: Institute of Medicine.|
|Low (BMI 19.8)||12.5–18||28–40|
|Normal (BMI of 19.8 to 26.0)||11.5–16||25–35|
|High (BMI 26.0 to 29.0)||7–11.5||15–25|
both in preconception and early pregnancy. Since studies indicate that most women get less than half the recommended amount of folic acid, the March of Dimes recommends women consider a supplement of 400 micrograms of folic acid preconceptually to prevent the incidence of neural tube defects. In addition, it is suggested women capable of becoming pregnant consume a diet high in folic acid. Good sources of folic acid include oranges, green leafy vegetables, and fortified bread and cereals.
There is also a direct correlation between ethnicity, age, marital status, and educational status with increased negative pregnancy outcomes, such as low birth weight.
Pregnancy Weight Gain
Pregnancy is divided into three trimesters, with each trimester lasting three months, or approximately thirteen weeks (a normal pregnancy lasts 40 weeks). Recommendations for weight gain during pregnancy are based on the Institute of Medicine (IOM) definitions of prepregnancy BMI range. The BMI is defined as weight in pounds, divided by height in inches, divided by height in inches, multiplied by 703 (or weight in kilograms, divided by height in centimeters, divided by height in centimeters, multiplied by ten-thousand). The majority of weight gain should occur in the second and third trimesters. Weight gain can vary greatly in normal pregnancies with normal birth outcomes. Few studies have included women in their first trimester, so the importance of first-trimester weight gain on pregnancy outcome is unclear. However, a slow and steady rate of weight gain is considered ideal. The current recommended weight gain for the BMI ranges are outlined in the accompanying figure.
Poor weight gain during pregnancy is associated with prematurity, low birth weight, and small for gestational age. Among normal-weight women, weight gain above the recommended level corresponds to maternal fat stores and is not of benefit to fetal growth. In other words, fat gain during pregnancy parallels gestational weight gain, and women with greater weight gain also gain more fat. In addition, an inverse relationship exists between pre-pregnancy BMI and weight gain during pregnancy: women with a low pre-pregnancy BMI tend to gain more weight than women with a high prepregnancy BMI. On average, overweight women gain less weight than their thinner counterparts, though it is not unusual for obese women to achieve normal birth outcomes with less than the recommended weight gain.
DAILY NUMBER OF SERVINGS SUGGESTED FOR PREGNANCY (Approximately 2200 calories)
|* Values for total fat and added sugars include fat and added sugars that are in food choices from the five major food groups, as well as fat and added sugars from foods in the fats, oils, and sweets group.|
|SOURCE: USDA Center for Nutrition Policy and Promotion.|
|Bread Group (one serving= 1 slice bread, ½ cup cereal, noodles, or rice)||9|
|Fruit Group (one serving = ½ cup fruit/fruit juice or one medium fruit)||3|
|Vegetables Group (One serving = ½ cup cooked or one cup raw)||4|
|Meat Group (one ounce chicken, beef, etc.)||6|
|Milk Group (one serving = 1 cup milk, 1 ounce cheese)||3|
|Total Fat (grams)*||73|
|Total added sugars (teaspoons)*||2|
In adolescent pregnancies, there are no established BMI recommendations regarding prepregnancy weight and weight gain. Excess weight gain, however, has been associated with postpartum obesity in adolescents.
Pregnancy Nutrition Requirements
Traditionally, caloric requirements during pregnancy have been estimated to be around an additional 300 calories per day. However, this must be adjusted for physical activity and prepregnancy weight (see accompanying figure) for the recommended number of servings of food groups). To meet weight-gain recommendations, a woman with a low prepregnancy BMI and a high activity level would require more calories than a woman with a high prepregnancy BMI and a sedentary lifestyle. A variety of foods from all food groups is important, since foods within the same food group do not contain exactly the same amount of nutrients. If increased weight gain is recommended, an emphasis should be placed on high-calorie food group items that contain a higher fat and sugar content. When less weight gain is recommended, women should choose from the lower-calorie food group choices.
Recommendations regarding sugar intake for pregnant women depend on weight gain and maternal blood glucose levels. A high sugar intake would not be advisable for women gaining more than the recommended weight or for those women who are having difficulty controlling normal blood glucose levels, while a high sugar intake would be beneficial for women requiring increased weight gain. A high sugar intake for women who are experiencing excessive weight gain or having difficulty maintaining normal glucose levels could result in increased maternal risk for complications associated with too much weight gain, such as diabetes, hypertension, premature delivery, and a large for gestational age fetus.
Adequate fluid intake is important to maintain hemodynamics (blood circulation) and homeostasis (fluid and tissue balance) and to reduce the risk of urinary tract infections. All pregnant women are encouraged to consume at least 64 ounces of fluid daily. Women at risk of gaining too much weight should be cautioned to limit their intake of sweetened fluids, including juice, and to consume more water. Exercise is considered healthful for most pregnant women, who should be encouraged to continue to exercise at prepregnancy levels. However, women should be cautious about
This human fetus is in the second trimester of development, a time when fetal weight gain begins to accelerate. Pregnant women should increase caloric intake by approximately 300 calories per day to account for rapid fetal growth. Calcium and iron supplements may also be necessary.
beginning any new exercise program during pregnancy, and, if medically advised, should avoid certain activities. Health care providers may recommend bed rest and limiting physical activity (such as work) when preterm labor is present or when weight gain is poor. Increased physical activity will control excess weight gain, in addition to the normal beneficial physical and emotional effects.
Vitamin and Mineral Requirements
Iron is the only recommended nutrient for which requirements cannot be reasonably met by diet alone during pregnancy. Thirty milligrams of ferrous iron is recommended, and iron should be taken on an empty stomach. When more than 30 mg of iron is given to treat anemia, it is suggested to also take approximately 15 mg of zinc and 2 mg of copper, since iron interferes with absorption and utilization of these materials.
According to some studies, caffeine decreases the availability of certain nutrients, such as calcium, zinc, and iron. Current recommendations, therefore, include limiting the consumption of caffeinated containing products.
Calcium supplementation may be suggested if the average daily intake of calcium is less than 600 mg. Calcium intake is of particular concern among pregnant women under the age of twenty-five, since bone mineral density is still increasing in these women. Calcium supplements, if recommended, should be taken with meals. Additionally, vitamin D may be necessary if sunlight exposure is minimal. For vegetarians, the current recommendations also include a daily supplement of 2 mg of Vitamin B12.
For women who don't ordinarily consume an adequate diet, or for those in high-risk categories (such as those carrying twins, heavy smokers, and drug abusers) a prenatal vitamin supplement is recommended, beginning in the second trimester. The supplement should contain the following: iron (30 mg); zinc (15 mg); copper (2 mg); calcium (250 mg); vitamin B6 (62 mg); folate (300 mg); vitamin C (50 mg); vitamin D (5 mg).
Special Nutrition Concerns
Food cravings during pregnancy are common and are not cause for concern, provided other nutrient needs are met and weight gain is in the target range. Pica—the ingestion of nonfood substances of nutritional value—is associated with anemia and can be a source of lead poisoning, bacterial infection, and dental problems. Pregnant women should be encouraged to avoid pica and discuss it with their medical provider.
Gestational diabetes is associated with high prepregnancy BMI and excess pregnancy weight gain. Infants of gestational-diabetic mothers are usually born large for gestational age (macrosomia) and are at higher risk for cesarean delivery and hypoglycemia postpartum.
Symptoms of toxemia of pregnancy, also known as preeclampsia, include swelling (edema) and proteinuria (excess protein in the urine). The cause of toxemia has not been determined, but the risk is associated with first pregnancies, advanced maternal age, African-American ethnicity, and women with a past history of diabetes, hypertension, or kidney disease. In severe cases, delivery is frequently induced.
Tips for common pregnancy discomforts include avoidance of offending foods (and their odor) when nausea and heartburn occur. Many pregnant women find that spicy, fatty foods can increase problems with nausea and heartburn. Frequent, small, and blander meals are often better tolerated. Some women find eating dry crackers before rising from bed in the morning helpful for nausea. However, since nausea and vomiting usually subside by the end of the first trimester, they do not have a significant impact on the final weight gain in most pregnancies. Hyperemesis gravidarum, or intractable vomiting during pregnancy, can rapidly result in dehydration, so medical intervention is required.
When constipation is a concern, increased consumption of whole grains, fruits, and vegetables is advisable, as well as increased fluid intake and physical activity.
Breastfeeding is the recommended method of infant nutrition, with a few exceptions. It benefits both mother and infant by providing protective antibodies to human disease, and breastfed babies are generally healthier and have higher I.Q. levels than bottle-fed babies. The development of jaw alignment problems and allergies are also far less likely in breastfed babies, while mothers who breastfeed have less postpartum complications and are considered to be at lower risk for breast cancer.
In the United States, women with HIV infection should not breastfeed. This is not a contraindication in developing countries, however, as the benefits may outweigh the possibility of infection. Untreated tuberculosis is also a contraindication for breastfeeding, while hepatitis C is currently not a contraindication for breastfeeding.
The Women, Infants, and Children (WIC) Program
The WIC program was established in the 1970s as a supplemental food and nutrition-education program. Eligibility requirements include a household income of up to 185 percent of the federal poverty level, as well as nutrition-risk criteria. The WIC program goals include improving pregnancy outcomes by helping participants achieve recommended weight gain. Nutritional food choices and calorie levels based on recommended weight gain are emphasized. The program has been shown to significantly reduce a number of negative pregnancy outcomes, including low birth weight.
Edwards, Cecile H. (1994) "African American Women and Their Pregnancies: Research Papers from the Program Project: Nutrition, Other Factors, and the Outcome of Pregnancy." Journal of Nutrition 124(6):917s–1027s.
Institute of Medicine, Committee on Nutritional Status during Pregnancy (1990). Nutrition during Pregnancy. Washington, DC: National Academy Press.
"Recent Developments in Maternal Nutrition and Their Implications for Practitioners." (1994). American Journal of Clinical Nutrition 59(2):437s–545S.
Stevens-Simon, Catherine, and McAarney, Elizabeth R. (1992). "Adolescent Pregnancy: Gestational Weight Gain and Maternal and Infant Outcomes." American Journal of Diseases of Children 146:1359–1364.
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March of Dimes. "Folic Acid." Available from <http://www.marchofdimes.com/professionals/690.asp>
March of Dimes. "National Perinatal Statistics." Available from <http://www.marchofdimes.com/professionals/680_1239.asp>
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National Institute of Child Health and Human Development (2002). "Understanding Gestational Diabetes." Available from <http://www.nichd.nih.gov>
United States Department of Agriculture (USDA) Center for Nutrition Policy. Available from <http://www.usda.gov/cnpp>