Key Abbreviations
American College of Obstetricians and Gynecologists ACOG
Body mass index BMI
Centers for Disease Control and Prevention CDC
Dietary Reference Intakes DRI
Docosahexaenoic acid DHA
Eicosapentaenoic acid EPA
Food and Drug Administration FDA
Institute of Medicine IOM
Neural tube defect NTD
Polyunsaturated fatty acid PUFA
Recommended Daily Allowance RDA
Resting metabolic rate RMR
Small for gestational age SGA
Thermic effect of energy TEE
Thermic effect of food TEF
Upper intake level UL
World Health Organization WHO
Women, Infants, and Children Program WIC
Overview
In light of the obesity epidemic, the concept of eating for two during pregnancy has come under great scrutiny in recent years. Despite public health efforts to promote weight loss, the number of reproductive-age women who are overweight (body mass index [BMI] >25.0 to 29.9 kg/m 2 ) has remained stable at approximately 30%. Of more concern is the twofold increase in obesity (BMI > 30 kg/m 2 ) from 13% to 35% in the same population ( Fig. 7-1 ). This increase in obesity disproportionately affects minority populations, such as Hispanics and blacks, and especially women. The increased rates of obesity are attributed to numerous factors that include increased consumption of nonnutritious foods and decreased physical activity. In pregnancy, excessive gestational weight gain increases the risk of higher BMI in a subsequent pregnancy.
Excessive weight gain during pregnancy significantly increases the risk of postpartum weight retention and contributes to the accretion of excess adipose tissue in the fetus. Additionally, obesity poses specific risks to the process of labor and delivery and to fetal outcomes. Obesity, however, is not the only concern in the management of nutrition during pregnancy. The importance of adequate nutrition is also a critical issue during pregnancy, and deficiency or excess of various nutrients can have both short- and long-term consequences to the mother and her fetus. In this chapter we address the specific nutrient requirements during pregnancy, recommendations for weight gain, and other special concerns regarding nutrition and pregnancy.
Integrating Nutrition Into the Obstetric History
Every woman should have the opportunity to meet with a health care provider for a prepregnancy history and physical examination that includes a nutritional assessment. The purpose of this assessment is to identify the quality of a patient’s diet and to assess any nutritional risk factors that could jeopardize her health or the health of her developing baby. Adequate intake of nutrients supports the developing fetus, reduces fetal risk, and improves pregnancy outcomes. During the nutritional assessment, the patient’s medical history, weight status, dietary intake, and laboratory data should be reviewed. The medical history will identify maternal risk factors for nutritional deficiencies and chronic diseases with nutritional implications (e.g., absorption, eating, and metabolic disorders; infections; inflammatory bowel disease; diabetes mellitus; phenylketonuria; sickle cell trait; and renal disease).
Pertinent dietary information includes appetite, meal patterns, dieting regimens, cultural or religious dietary practices, dietary restrictions, food allergies, cravings, and aversions. Information about abnormal eating practices such as bingeing, purging, laxative or diuretic use, or pica—eating nonfood items (ice, detergent, starch)—should be ascertained.
During the assessment, other relevant information includes the habitual use of caffeine-containing beverages or sugary soft drinks, tobacco, alcohol, recreational drugs, vitamins, and herbal supplements. Specifically asking about nutritional supplements is critically important because many patients do not consider these items to be “medications” and thus will not volunteer that these are being used. A patient’s diet can be assessed by asking about intake over the previous 24 hours or by administering a diet history questionnaire in the waiting room.
Nutrition-related complications during a prior pregnancy are also important to assess. Gestational weight gain in previous pregnancies and history of hyperemesis, gestational diabetes, anemia, and pica should be determined (see Chapters 6 and 40 ). Women with a short interpregnancy interval (e.g., <1 year between pregnancies) may have depleted nutrient reserves, which is associated with increased preterm birth, intrauterine growth restriction (IUGR), and maternal morbidity and mortality.
In addition to the medical history, the social history may provide key information regarding the patient’s nutritional risk. For example, some work environments adversely impact dietary intake because they may not provide adequate time to eat balanced meals, or they allow access to food that is only marginally nutritious. Women with lower socioeconomic status often need support to obtain nutritious food, and referral to food-assistance programs may be appropriate (e.g., Women, Infants, and Children Program [WIC]).
Many women are receptive to nutritional counseling just prior to or during pregnancy, making this an opportune time to encourage the development of good nutrition and physical activity practices aimed at preventing future medical problems such as obesity, diabetes, hypertension, and osteoporosis. Pregnant women found to be at risk may benefit from a referral to a registered dietitian as shown in Table 7-1 .
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Maternal Weight Gain Recommendations
In 1990 the Institute of Medicine (IOM) first published recommendations on weight gain during pregnancy. The guidelines were proposed to address many issues regarding the role of nutrition in pregnancy, including the prevention of small-for-gestational-age (SGA) and growth-restricted neonates. As noted previously, the obesity rate has surged in recent decades. As such, in 2009, the IOM updated the 1990 guidelines regarding weight gain in pregnancy. In contrast to the 1990 recommendations, these guidelines consider both the short- and long-term outcome for the pregnant woman and her child. Additionally, because of the great importance of achieving appropriate pregravid weight, the 2009 guidelines emphasize that women begin pregnancy at a healthy weight. Lastly, the guidelines call for individualized preconceptual, prenatal, and postpartum care to help women attain healthy weight gain and return to a healthy pregravid weight after delivery.
Many general recommendations exist regarding diets for pregnant women to avoid problems such as excessive gestational weight gain and potential complications such as gestational diabetes and fetal overgrowth. These diets vary from those high in complex carbohydrates and low in fats to those low on the glycemic index to diets high in probiotics. Whereas all of these diets may offer some theoretic advantage, presently none can be endorsed as optimal. Consuming healthy food is the goal to meet the IOM gestational weight guidelines and address the individual needs of the patient.
Low or Underweight Preconception Body Mass Index
The 2009 IOM guidelines are based upon the World Health Organization (WHO) classifications to define underweight, normal weight, overweight, and obese patients ( Table 7-2 ). Underweight is classified as a BMI below 18.5 kg/m 2 . Based on the available data, there is strong support that women with low pregnancy BMI and low gestational weight gain have an increased risk (<10%) for having SGA infants, preterm birth, and perinatal mortality. In contrast, excessive gestational weight gain for women with a low pregravid BMI increases risk of large-for-gestational-age (LGA) neonates and for increased maternal weight retention postpartum ( Fig. 7-2 ; also see Chapters 6 and 41 ).
| PREGNANCY BMI | BMI (kg/m 2 ) | TOTAL WEIGHT GAIN (lb) | RATES OF WEIGHT GAIN IN SECOND AND THIRD TRIMESTERS (lb/wk) |
|---|---|---|---|
| Underweight | <18.5 | 28-40 | 1 (1-1.3) |
| Normal weight | 18.5-24.9 | 25-35 | 1 (0.8-1) |
| Overweight | 25.0-29.9 | 15-25 | 0.6 (0.5-0.7) |
| Obese (all classes) | ≥30.0 | 11-20 | 0.5 (0.4-0.6) |
Overweight and Obese Prepregnancy Body Mass Index
Approximately 60% of reproductive-age women are overweight (BMI >25 kg/m 2 ), and of these, 50% are obese (BMI >30 kg/m 2 ). Another 8% have severe obesity, with a BMI greater than 40 kg/m 2 . Obesity poses a multitude of threats related to pregnancy: antepartum risks include spontaneous abortion, congenital anomalies, preterm birth, gestational diabetes, hypertension, and preeclampsia; during labor, risk of shoulder dystocia and cesarean delivery are higher; and postpartum risks include thromboembolic events, anemia, and incision-site infections (see Chapters 6 and 41 ).
The 2009 IOM guidelines recommend that overweight women with a singleton pregnancy gain a total of 15 to 25 lb during pregnancy (compared with 25 with 35 lb for normal-weight women). Obese women are advised to gain only 11 to 20 lb during the course of their pregnancy. These recommendations were based primarily on class I obesity because data are limited regarding weight gain recommendations for each class of obesity. As such, the IOM guidelines do not differentiate between class I obesity (BMI 30 to 34.9 kg/m 2 ), class II obesity (BMI 35 to 39.9 kg/m 2 ), and class III obesity (BMI ≥40 kg/m 2) . The 11 to 20 lb gestational weight gain for obese patients primarily represents the obligatory weight gain of pregnancy. This includes approximately 12 to 14 lb of water, 2 lb of protein, and a variable amount of adipose tissue ( Table 7-3 ).
| GRAMS | |
|---|---|
| Protein | |
| Fetus | 420 |
| Uterus | 170 |
| Blood | 140 |
| Placenta | 100 |
| Breasts | 80 |
| Total | 900-1000 |
| Water | |
| Fetus | 2400 |
| Placenta | 500 |
| Amniotic fluid | 500 |
| Uterus | 800 |
| Breasts | 300 |
| Maternal blood | 1300 |
| Extracellular fluid | 1500 |
| Total | 7000-8000 |
| Variable Components of Weight Gain | |
| Carbohydrate | Negligible |
| Lipids | 0-6 kg |
Some authors have recommended less gestational weight gain for obese class II and III women to decrease neonatal morbidity. Whereas others have noted an increased risk of SGA babies with decreased lean body mass, as well as decreased fat mass, in overweight and obese women with inadequate gestational weight gain.
Maternal Weight Gain Recommendations for Special Populations
Multiple Gestations
For twin pregnancies, the IOM recommends a gestational weight gain of 37 to 54 lb for women of normal weight, 31 to 50 lb for overweight women, and 25 to 42 lb for obese women ( Table 7-4 ). For triplet and higher-order gestations, the data on ideal gestational weight gain are insufficient; thus no specific recommendations exist for these.
| PREPREGNANCY BMI | BMI (kg/m 2 ) | TOTAL WEIGHT GAIN (lb) |
|---|---|---|
| Normal weight | 18.5-24.9 | 37-54 |
| Overweight | 25.0-29.9 | 31-50 |
| Obese | ≥30.0 | 25-42 |
Adolescents
Approximately 17% of teenage girls ages 12 through 19 are obese in America, and these obese teens face the same obstetric risks that adult obese women face. Because 80% of teen pregnancies are unintended, the ability of an obstetrician to discuss preconception nutrition concerns with an obese teen is nearly impossible. Thus efforts should be made during the early prenatal care visits to emphasize the importance of appropriate gestational weight gain and adequate nutrition. Studies have shown that teens who are obese before conceiving are more likely to remain obese postpartum. The IOM recommendations state that adolescents should follow the adult BMI categories to guide their weight gain.
Other Groups
Based on the available evidence, no specific recommendations exist for gestational weight gain in women of short stature, for specific racial or ethnic groups, or in those who smoke cigarettes. The IOM guidelines recognize that each of these special groups may possibly benefit from specific gestational weight gain guidelines, but the available evidence is insufficient to make recommendations.
Maternal Nutrient Needs: Current Recommendations
Energy
Energy expenditure consists of four basic components: (1) resting metabolic rate (RMR); (2) the thermic effect of food (TEF), or diet-induced thermogenesis; (3) the thermic effect of energy (TEE); and (4) adaptive, or facultative, thermogenesis. RMR is the amount of energy, or calories, used at rest and accounts for approximately 60% of total energy expenditure in healthy people. TEF is the caloric cost of eating, digesting, absorbing, resynthesizing, and storing food and accounts for about 5% to 10% of total energy expenditure. TEE is quite variable and in sedentary individuals may account for only 15% to 20% of total energy expenditure. Adaptive thermogenesis, or facultative thermogenesis, refers to adaptations by an organism to adjust to environmental changes, such as overfeeding or underfeeding, as well as to alterations in ambient temperature. Adaptive thermogenesis accounts for no more that 10% of RMR and varies by individual ( Fig. 7-3 ).
The total maternal energy requirement for a full-term pregnancy is estimated at 80,000 kilocalories (kcal). This accounts for the increased metabolic activity of the maternal and fetal tissues as well as for the growth of the fetus and placenta. Maternal energy needs are increased to support the maternal cardiovascular, renal, and respiratory systems. Basal requirements can be determined based on maternal age, stature, activity level, preconception weight, BMI, and gestational weight gain goals. Daily caloric requirements have been estimated by the WHO by dividing the gross energy cost of pregnancy (80,000 kcal) by the approximate duration of pregnancy (250 days after the first month), producing an average additional 300 kcal/day for the entire pregnancy. During the first trimester, total energy expenditure does not change greatly, and weight gain is minimal assuming the woman began her pregnancy without depleted body reserves. Therefore additional energy intake is recommended primarily in the second and third trimesters. During the second trimester, a pregnant woman should consume an additional 340 kcal/day above the nonpregnant energy requirement, and in the third trimester, the additional caloric requirement is 452 kcal/day.
However, a series of prospective studies were conducted in the late 1980s and 1990s to assess energy expenditure in pregnancy. Many of these studies obtained baseline data prior to a planned pregnancy and incorporated measurements such as estimates of body composition, energy intake in the diet, RMR, standard measures of exercise, and activity diaries. These studies showed that the energy cost of pregnancy is much lower than previously estimated.
The introduction of the doubly labeled water method has allowed researchers to estimate total energy expenditure in the free-living state. In well-nourished women, RMR usually begins to rise soon after conception and continues to rise until delivery. However, considerable interindividual variation is apparent. In healthy, well-nourished women, the average increases in RMR above prepregnancy values are 4.5%, 10.8%, and 24.0% for the first, second, and third trimesters, respectively.
Pregnancy induces changes in fuel utilization. Later in pregnancy, the basal or fasting contribution of carbohydrates to oxidative metabolism increases. Fetal growth and lactation are dependent on energy preferentially derived from carbohydrates.
Proteins
Additional protein is required during pregnancy for fetal, placental, and maternal tissue development. During the course of the pregnancy, an average of 925 g of protein are stored, which is required for the tissue development. Maternal protein synthesis increases to support expansion of the blood volume, uterus, and breast tissue. Fetal and placental proteins are synthesized from amino acids supplied by the mother. Protein recommendations are therefore increased from 46 g/day for an adult, nonpregnant woman to 71 g/day during pregnancy. This represents a change in protein recommendation from 0.8 g/kg/day for nonpregnant women to 1.1 g/kg/day during pregnancy.
Omega-3 Fatty Acids
Polyunsaturated fatty acids (PUFAs) are an essential component of neural tissue and are found in high concentrations in membrane phospholipids of the gray matter and the retina. These critically important fatty acids cannot be synthesized by the body and thus must be consumed in the diet as either linoleic or α-linolenic acid. After ingestion, α-linoleic acid is converted to its biologically active forms, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The amount of fatty acids that are transported to the fetus depends both on maternal dietary intake and placental function. With n-3 PUFA supplementation, randomized, placebo-controlled studies have shown a positive relationship between maternal intake and umbilical cord concentrations.
The best dietary sources for PUFAs are seafood—namely, oily fish such as salmon, sardines, and anchovies—as well as oils from some plants, such as flax seeds and walnuts. The Food and Drug Administration (FDA) recommends that pregnant women consume 200 to 300 mg/day of DHA, which can be achieved by consuming 1 to 2 servings (8 to 12 ounces) of fish per week. However, the average pregnant or lactating woman consumes only 52 mg/day of DHA and 20 mg/day of EPA. For those women with insufficient seafood consumption, alternate sources of DHA include fish oil supplements (150 to 1200 mg/day), enhanced prenatal vitamins (200 to 300 mg/day), DHA-enriched eggs (up to 150 mg/egg), and the plant oils listed above. Regarding seafood consumption, the American College of Obstetricians and Gynecologists (ACOG) encourages women who are pregnant, planning to become pregnant, or breastfeeding to follow the updated FDA recommendations to avoid fish with the highest mercury concentration, specifically tilefish, shark, swordfish, and king mackerel. They should also limit consumption of white albacore tuna to 6 oz/week.
During the third trimester of pregnancy and the first 2 years of infancy, brain development occurs rapidly, and DHA supplementation has been well studied during this period. The best evidence in support of PUFA supplementation comes from studies that show a positive relationship between PUFA supplementation and neurodevelopmental outcomes in children. Results of randomized, controlled trials have generally supported these findings. For example, one study used cod liver oil supplementation from 18 weeks gestational age until 12 weeks postpartum and found children’s mental processing scores at 4 years of age correlated significantly with maternal intake of DHA. However, other randomized, controlled trials have found no difference in cognitive and language scores between offspring of women supplemented with fish oil during pregnancy and those who received placebo. A recently published follow-up study showed that at 18 months of age, children of mothers who were supplemented with 800 mg of DHA during pregnancy showed no difference in mean cognitive, language, or motor scores, although fewer children in the DHA group had delayed development compared with controls.
In addition to the well-studied effects of PUFA on fetal brain development, much interest has been paid to other potential benefits of DHA supplementation during pregnancy. For instance, dietary supplementation with PUFA has been promoted as a means to prolong gestation and prevent prematurity. This hypothesis originated after an epidemiologic study compared the diets of women in Denmark to those of the Faroe Islanders, and researchers noted that the seafood-based diet of the island population was associated with higher birthweight (+225 g) at term. This association spawned subsequent research; however, a Maternal Fetal Medicine Network trial did not find evidence that fish oil supplementation decreased the risk of preterm delivery in high-risk patients. However, moderate fish intake of up to three meals/week before 22 weeks gestation was associated with a decreased risk of preterm birth. Although older trials of PUFA supplementation purported an increase in birthweight because of prolonged gestational age, more recent trials have reported a decrease in birthweight after adjusting for gestational age. Thus at present, evidence is insufficient to recommend PUFA supplementation as a means to reduce the risk of preterm birth.
Vitamin and Mineral Supplementation Guidelines
Dietary Reference Intakes
To address the changing nutritional needs of the American population, the Food and Nutrition Board of the IOM established the first Dietary Reference Intakes (DRIs) in 1997. These values moved beyond the traditional Recommended Daily Allowances (RDAs) to focus on the prevention of chronic disease, and the DRIs provide a range for safe and appropriate intake, as well as tolerable upper limit, based on the available research. The DRIs include four dietary reference values for every life stage and gender group. These include (1) estimated average requirement, (2) recommended dietary allowance, (3) adequate intake, and (4) tolerable upper intake level (UL). At present, DRIs have been established for vitamin A, the carotenoids, the B vitamins, vitamin C, vitamin D, vitamin K, folate, calcium, choline, chromium, copper, fluoride, iodine, iron, magnesium, manganese, molybdenum, phosphorus, biotin, pantothenic acid, selenium, and zinc. Recommendations regarding the intake of other nutrients will be available over the next decade as the scientific evidence is evaluated ( Table 7-5 ).
| VITAMIN/MINERAL | AGE (yr) | NONPREGNANT | PREGNANT | UPPER INTAKE LEVELS |
|---|---|---|---|---|
| Vitamin A (µg) | <18 | 700 | 750-1200 | 2800 |
| 19-30 | 700 | 770-1300 | 3000 | |
| 31-50 | 700 | 770-1300 | 3000 | |
| Vitamin C (mg) | <18 | 65 | 80 | 1800 |
| 19-30 | 75 | 85 | 2000 | |
| 31-50 | 75 | 85 | 2000 | |
| Vitamin D (µg) | <18 | 15 | 15 | 100 |
| 19-30 | 15 | 15 | 100 | |
| 31-50 | 15 | 15 | 100 | |
| Vitamin E (mg) | <18 | 15 | 15 | 800 |
| 19-30 | 15 | 15 | 1000 | |
| 31-50 | 15 | 15 | 1000 | |
| Vitamin K (µg) | <18 | 75 | 75 | ND |
| 19-30 | 90 | 90 | ND | |
| 31-50 | 90 | 90 | ND | |
| Thiamin (mg) | <18 | 1.1 | 1.4 | ND |
| 19-30 | 1.1 | 1.4 | ND | |
| 31-50 | 1.1 | 1.4 | ND | |
| Riboflavin (mg) | <18 | 1.1 | 1.4 | ND |
| 19-30 | 1.1 | 1.4 | ND | |
| 31-50 | 1.1 | 1.4 | ND | |
| Niacin (mg) | <18 | 14 | 18 | 30 |
| 19-30 | 14 | 18 | 35 | |
| 31-50 | 14 | 18 | 35 | |
| Vitamin B 6 (mg) | <18 | 1.2 | 1.9 | 80 |
| 19-30 | 1.3 | 1.9 | 100 | |
| 31-50 | 1.3 | 1.9 | 100 | |
| Folate (µg) | <18 | 400 | 600 | 800 |
| 19-30 | 400 | 600 | 1000 | |
| 31-50 | 400 | 600 | 1000 | |
| Vitamin B 12 (µg) | <18 | 2.4 | 2.6 | ND |
| 19-30 | 2.4 | 2.6 | ND | |
| 31-50 | 2.4 | 2.6 | ND | |
| Pantothenic acid (mg) | <18 | 5 | 6 | ND |
| 19-30 | 5 | 6 | ND | |
| 31-50 | 5 | 6 | ND | |
| Biotin (µg) | <18 | 25 | 30 | ND |
| 19-30 | 30 | 30 | ND | |
| 31-50 | 30 | 30 | ND | |
| Choline (mg) | <18 | 400 | 450 | 3000 |
| 19-30 | 425 | 450 | 3500 | |
| 31-50 | 425 | 450 | 3500 | |
| Calcium (mg) | <18 | 1300 | 1300 | 3000 |
| 19-30 | 1000 | 1000 | 2500 | |
| 31-50 | 1000 | 1000 | 2500 | |
| Chromium (µg) | <18 | 24 | 29 | ND |
| 19-30 | 25 | 30 | ND | |
| 31-50 | 25 | 30 | ND | |
| Copper (µg) | <18 | 890 | 1000 | 8000 |
| 19-30 | 900 | 1000 | 10000 | |
| 31-50 | 900 | 1000 | 10000 | |
| Fluoride (mg) | <18 | 3 | 3 | 10 |
| 19-30 | 3 | 3 | 10 | |
| 31-50 | 3 | 3 | 10 | |
| Iodine (µg) | <18 | 150 | 220 | 900 |
| 19-30 | 150 | 220 | 1100 | |
| 31-50 | 150 | 220 | 1100 | |
| Iron (mg) | <18 | 15 | 27 | 45 |
| 19-30 | 18 | 27 | 45 | |
| 31-50 | 18 | 27 | 45 | |
| Magnesium (mg) | <18 | 360 | 400 | 350 |
| 19-30 | 310 | 350 | 350 | |
| 31-50 | 320 | 360 | 350 | |
| Phosphorous (mg) | <18 | 1250 | 1250 | 4000 |
| 19-30 | 700 | 700 | 4000 | |
| 31-50 | 700 | 700 | 4000 | |
| Selenium (µg) | <18 | 55 | 60 | 400 |
| 19-30 | 55 | 60 | 400 | |
| 31-50 | 55 | 60 | 400 | |
| Zinc (mg) | <18 | 9 | 12 | 34 |
| 19-30 | 8 | 11 | 40 | |
| 31-50 | 8 | 11 | 40 |
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