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Maternal Nutrition


Sufficient intake of nutrients during pregnancy is essential to meet the demands of fetal growth and development as well as maternal physiologic adaptations to pregnancy. The nutritional status of pregnant women in the United States is suboptimal , owing to many factors, including access to and price of healthy foods, knowledge of a healthful diet, and pressing needs that may take priority over a healthful diet. Although too few pregnant women are included in national surveys to evaluate maternal dietary trends, a recent analysis of data from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (nuMoM2b) cohort, an observational study including eight centers, found that periconceptional diet quality is poor. On average, none of the scores for the 12 components of the Dietary Guidelines for Americans met current recommendations. Consumption of whole grains, dairy products, and fatty acids was especially low, whereas consumption of empty calories and sodium was too high. The foods that contributed most to energy intake were low in nutrients and rich in added sugars and solid fats, and primary sources of iron, folate, and vitamin C were juices and enriched breads.

Obesity compounds the problem of poor dietary quality in the United States. In 2019, prepregnancy obesity affected 29% of women, up from 26% in 2016. Equally as concerning is that 11% of US women have a body mass index (BMI) of 40 kg/m 2 or more. The prevalence of women living with class 3 obesity has more than tripled since 1970 and is forecasted to increase in the next decade. Almost 50% of pregnant women in the United States gain more weight than is recommended, and 20% gain too little.

Poor maternal nutritional status is problematic because it has a powerful influence on the offspring’s health and susceptibility to disease later in life. In utero exposure to undernutrition or overnutrition is associated with poor health outcomes in adulthood, including metabolic disease, obesity, cancer, and osteoporosis. , Numerous poor pregnancy and birth outcomes have been associated with nutritional deficiencies, including preterm birth, fetal growth restriction (FGR), gestational diabetes mellitus (GDM), and preeclampsia. Nutritional status may have a critical influence in the periconceptional period, when fetal growth trajectory, placental capacity to supply nutrients to the fetus, fetoplacental immunology and inflammation, and maternal hormonal and metabolic regulatory systems are established. A poor-quality diet during pregnancy also threatens maternal health by promoting obesity, , excessive gestational weight gain (GWG), and postpartum weight retention. All clinicians caring for reproductive-age women should educate themselves and their patients about the importance of good nutritional health before, during, and after pregnancy.

What Is Healthy Eating During Pregnancy?

The 2020 Dietary Guidelines for Americans is a guide to help all individuals consume a healthy diet that meets nutritional needs. This edition, for the first time, provides guidelines by life stage, including pregnancy and lactation. Though the nutrition recommendations for pregnant people mirror those of the general US population, the guidelines have specific recommendations for nutrients for pregnant or lactating people, specifically folate, iron, iodine, choline, seafood, alcoholic beverages, and caffeine. These are discussed in greater detail later in the chapter.

The focus of the Dietary Guidelines is disease prevention and health promotion. Importantly, the recommendations focus on eating patterns rather than consumption of individual nutrients or foods, because increasing data point to the importance of overall dietary patterns in prevention of adverse health outcomes. The Dietary Guidelines focus on four concrete steps to achieve a healthy diet. These include: (1) follow a health dietary pattern at every life stage; (2) customize and enjoy nutrient-dense food and beverage choices to reflect personal preferences, cultural traditions, and budgetary considerations; (3) focus on meeting food group needs with nutrient-dense foods and beverages and stay within calorie limits; and (4) limit foods and beverages higher in added sugars, saturated fat, and sodium. Key recommendations for healthy eating patterns provided by the Dietary Guidelines are shown in Box 12.1 , and examples of foods in each food group are shown in Table 12.1 .

Box 12.1
Key Recommendations for Healthy Eating Patterns According to the Dietary Guidelines for Americans

  • Consume a healthy eating pattern that accounts for all food and beverages within an appropriate calorie level.

  • A healthy eating pattern includes:

    • A variety of vegetables from all of the subgroups (dark green, red and orange, legumes [beans and peas], starches, and other)

    • Fruits, especially whole fruits

    • Grains, at least half of which are whole grains

    • Fat-free or low-fat dairy, including milk, yogurt, cheese, or fortified soy beverages

    • A variety of protein foods, including seafood; lean meats and poultry; eggs; legumes (beans and peas); and nuts, seeds, and soy products

    • Oils

  • A healthy eating pattern limits saturated and trans fats, added sugars, and sodium:

    • Consume less than 10% of calories/day from added sugars

    • Consume less than 10% of calories/day from saturated fats

    • Consume less than 2300 mg/day of sodium

TABLE 12.1
Examples of Foods From Each Food Group
Vegetable Group Fruit Group Grains Group Protein Group Dairy Group
Carrots
Sweet potatoes
Pumpkin
Spinach
Cooked greens (e.g., kale, collard greens)
Winter squash
Tomatoes and tomato sauces
Red sweet peppers		 Melons (e.g., cantaloupe, honeydew)
Mangos
Prunes
Bananas
Apricots
Oranges
Berries
100% prune juice or orange juice		 Fortified ready-to-eat cereals
Fortified cooked cereals (e.g., oatmeal)
Whole-wheat bread
Brown rice
Pasta
Tortillas		 Beans and peas (e.g., pinto beans, soybeans, white beans, lentils, chickpeas)
Nuts and seeds (e.g., sunflower seeds, almonds, walnuts, peanuts, peanut butter)
Lean beef, lamb, and pork
Poultry
Fish and seafood		 Fat-free or low-fat yogurt
Fat-free milk (skim milk)
Low-fat milk (1% milk)
Calcium-fortified nut milk (e.g., soy milk)

Pregnant women can put the Dietary Guidelines for Americans into practice using a tool called MyPlate. MyPlate illustrates the five food groups that make up a healthy eating plan and in what proportions they should appear on the plate. The MyPlate Plan ( https://www.myplate.gov/widgets-sm/myplate-daily-checklist-input-start ) is an interactive resource for pregnant women and health care professionals to calculate what and how much to eat within the recommended calorie allowance. The dietary advice is tailored based on age, sex, weight, height, and physical activity. Women are asked whether they are pregnant or breastfeeding, and if they indicate pregnant, they are asked what trimester in gestation and their prepregnancy weight. Once the MyPlate Plan is generated, it illustrates how many foods in each food group should be eaten daily as well as limits on sodium, saturated fat, and added sugars. MyPlate encourages intake of 40% vegetables, 10% fruit, 20% protein, and 30% grains, along with a serving of dairy at each meal. Food choices are often limited by financial considerations. The MyPlate resource also includes an interactive tool that is designed for low-income families ( https://www.myplate.gov/budget ). Another useful resource for general prenatal dietary guidelines is provided by the March of Dimes ( www.marchofdimes.com/pregnancy/nutrition_indepth.html ).

A useful resource to assist clinicians in calculating nutrient recommendations for dietary planning is the DRI Calculator for Healthcare Professionals ( https://www.nal.usda.gov/fnic/interactiveDRI/ ). This website is an interactive tool that clinicians can use to calculate estimated energy requirement and recommended micronutrient and macronutrient intakes for their patients. In the first trimester of pregnancy, energy requirements are similar to requirements for nonpregnant women. Energy needs increase by approximately 340 kcal and 450 kcal in the second and third trimesters, respectively. Slight modifications to these energy needs are based on activity level, prepregnancy weight, and age. Table 12.2 shows the Dietary Reference Intake values and the MyPlate Daily Plan for a 26-year-old woman in the second trimester of pregnancy with a prepregnancy weight of 140 lb (64 kg) and a height of 68 inches (1.7 m). A complete table of all DRI for pregnant women by age and trimester is available in the Dietary Guidelines for Americans 2020 report. ,

TABLE 12.2
Example Nutrient Requirements and MyPlate Food Group Amounts for a 26-Year-Old Woman in Her Second Trimester Who Is Sedentary and Had a Prepregnancy Weight of 140 lb and Height of 68 Inches
Dietary Reference Intakes, Amounts per Day, Estimated Energy Requirement (Second Trimester): 2330 kcal/day MyPlate Daily Plan, Amounts per Day for 2400-cal/day Diet
Macronutrients

  • Carbohydrate: 262–379 g

  • Protein: 70 g

  • Total fat: 52–91 g

  • Fiber: 28 g

Vitamins

  • Vitamin A: 770 μg

  • Vitamin C: 85 mg

  • Vitamin D: 15 μg

  • Vitamin E: 15 mg

  • Thiamine: 1 mg

  • Riboflavin: 1 mg

  • Niacin: 18 mg

  • Vitamin B 6 : 6 mg

  • Vitamin B 12 : 3 μg

  • Folate: 600 μg

  • Choline: 450 mg

Minerals

  • Calcium: 1000 mg

  • Copper: 1000 μg

  • Iron: 27 mg

  • Magnesium: 350 mg

  • Potassium: 4.7 g

  • Selenium: 60 μg

  • Sodium: 1.5 g

  • Zinc: 11 mg

Fruit: 2 cups

  • 1 cup of fruit counts as:

    • 1 cup raw or cooked fruit or

    • ½ cup dried fruit or

    • 1 cup 100% fruit juice

Vegetables: 3 cups

  • 1 cup vegetables counts as:

    • 1 cup raw or cooked vegetables or

    • 2 cups leafy salad greens or

    • 1 cup 100% vegetable juice

Grains: 8 oz (≥4 oz whole grain)

  • 1 oz of grains counts as:

    • 1 slice of bread or

    • 1 oz ready-to-eat cereal or

    • ½ cup cooked rice, pasta, or cereal

Protein: 6.5 oz

  • 1 oz of protein counts as:

    • 1 oz lean meat, poultry, or seafood or

    • 1 egg or

    • 1 Tbsp peanut butter or

    • ¼ cup cooked beans or peas or

    • ½ oz nuts or seeds

Dairy: 3 cups

  • 1 cup of dairy counts as:

    • 1 cup milk or

    • 1 cup yogurt or

    • 1 cup fortified soy beverage or

    • 1½ oz natural cheese or 2 oz processed cheese

Limit sodium to 2300 mg/day
Limit saturated fat to 27 g/day
Limit added sugars to 60 g/day

Dietary Supplement Use

The Centers for Disease Control and Prevention (CDC) recommends that women who are capable of becoming pregnant consume 400 μg/day of synthetic folic acid from fortified food (cereals and other grains), supplements, or both in addition to consuming folate from foods in a varied diet. , The same group recommends 30 mg/day of iron starting early in pregnancy. These are universal recommendations. Women who consume nutritious diets may not require multiple micronutrient supplementation during pregnancy. The National Academy of Medicine (formerly the Institute of Medicine [IOM] and the CDC recommend dietary supplementation for women with a poor diet. Given the prevalence of poor nutrition and the resources required to do a detailed dietary assessment, however, universal multivitamin supplementation in the form of prenatal vitamins is routine. There are particular women at high risk for inadequate nutrition, including women with multiple gestations, adolescents, women who consume a vegan diet, women with substance use disorder, and women with malabsorption syndrome or history of gastric bypass, in whom evaluation and supplementation are particularly important.

Evidence supporting the use of multivitamin supplementation during pregnancy is derived largely from low-income and middle-income countries and may be less relevant to high-income countries such as the United States. A Cochrane review published in 2015 concluded that supplementation decreased the risk of small-for-gestational-age (SGA) infants (relative risk [RR] = 0.90; 95% confidence interval [CI], 0.83–0.97), low-birth-weight infants (RR = 0.88; 95% CI, 0.85–0.91), and stillbirth (RR = 0.91; 95% CI, 0.85–0.98). There were no significant differences in other maternal and perinatal outcomes.

Additional information about specific nutrients follows.

Folate

Folate is a term used to describe both folate that occurs naturally in food sources and folic acid, the form of the vitamin found in fortified foods and dietary supplements. Folate is essential for nucleic acid synthesis, red blood cell synthesis and maintenance, and fetal and placental growth. Maternal folic acid deficiency can cause neural tube defects (NTDs) in the fetus and other congenital anomalies. As noted earlier, the CDC recommends 400 μg/day of folic acid from diet or supplements for all women capable of becoming pregnant to reduce the risk for NTDs. This is similar to the United States Preventive Services Task Force (USPSTF), which recommends a daily supplement of 400 to 800 μg of folic acid. Box 12.2 shows folate-rich foods and the amount of folate per serving, but it is important to note that the recommendation for folic acid supplementation is in addition to folate consumed with a healthy diet. Women with a previous pregnancy affected by an NTD should take 4 mg of folic acid beginning 1 month before conception and throughout the first trimester. The United States began mandatory fortification of cereal and grain products with folic acid in 1998. Fortification substantially improved the folate status of US women of childbearing age and reduced the incidence of pregnancies affected by NTDs by 25%. However, there is concern that folic acid supplementation may no longer further reduce risk of NTDs because fortification may provide the amount of folic acid required to prevent most folate-sensitive NTDs. ,

Box 12.2
Folate-Rich Foods a

a Recommended Dietary Allowance 600 μg/day.

Modified from US Department of Agriculture, Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Release 28, 2016. https://ndb.nal.usda.gov/ndb/ .

  • 100–150 μg folate per serving

    • Beef liver, 3 oz

    • Spinach, cooked, ½ cup

    • Black-eyed peas, cooked, ½ cup

    • Breakfast cereals, fortified with 25% of daily value for folate, 1 serving

  • 50–99 μg folate per serving

    • Rice or pasta, cooked, ½ cup

    • Green leafy vegetables (asparagus, broccoli, collard greens, Brussels sprouts), cooked, ½ cup

    • Romaine lettuce or spinach (raw), 1 cup

    • Avocado, ½ cup

  • 20–49 μg folate per serving

    • Green peas, cooked, ½ cup

    • Kidney or other beans, cooked, ½ cup

    • Orange juice or tomato juice, ¼ cup

    • Banana, 1 medium

    • Egg, 1 large

    • Bread, 1 slice

    • Peanuts, 1 oz

Folate deficiency has also been associated with a number of adverse birth outcomes, including spontaneous preterm birth. , Folic acid supplementation in pregnancy has been shown to lengthen gestation in some, but not all, studies. There has been no decline in the prevalence of preterm birth since nationwide folic acid fortification was instituted. It is possible that the relative concentrations of folate species, which mediate the varied biologic effects of folate, may prove more critical than total folate concentration in preventing preterm birth.

Vitamin D

Vitamin D is a prohormone that is either ingested orally through diet or supplements or is produced photochemically in the skin. Vitamin D has diverse biologic functions, and it has relevance beyond bone health and calcium metabolism. Vitamin D deficiency jeopardizes maternal and fetal bone mass, but the association between vitamin D and adverse birth outcomes remains equivocal.

There is significant controversy surrounding vitamin D in pregnancy, including the ideal concentration of serum 25-hydroxyvitamin D [25(OH)D], the best clinical marker of vitamin D nutritional status. In 2010, the IOM increased the recommended dietary intake for vitamin D in pregnancy from 200 IU to 600 IU in an effort to ensure a serum 25(OH)D level of approximately 50 nmol/L in most of the population. However, the Endocrine Society and many individual experts argue that optimal 25(OH)D concentrations are 75 to 100 nmol/L and that maintaining these levels requires at least 1000 IU/day in nonpregnant adults , and 4000 IU/day for pregnant women.

The American College of Obstetricians and Gynecologists (ACOG) noted that there is insufficient evidence to support universal screening of pregnant women for vitamin D deficiency. ACOG states clinicians may consider screening women “at increased risk” for vitamin D deficiency but does not recommend universal supplementation. If blood levels reveal deficiency, ACOG states that a dose of 1000 to 2000 IU/day of vitamin D is considered safe. Table 12.3 shows food sources rich in vitamin D and the amount per serving.

TABLE 12.3
Food Sources of Vitamin D (Recommended Dietary Allowance: 600 IU/day)
From US Department of Agriculture, Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Release 28, 2016. https://ndb.nal.usda.gov/ndb/ .
Foods Approximate IU per Serving
Cod liver oil, 1 Tbsp 1400
Salmon (sockeye), 3 oz 450
Tuna fish, canned, 3 oz 150
Orange juice, vitamin D–fortified, 8 oz a 140
Milk, vitamin D–fortified, 8 oz a 110–130
Yogurt, vitamin D–fortified, 6 oz a 80
Margarine, vitamin D–fortified, 1 Tbsp a 60
Beef liver, 3 oz 40
Egg, 1 large 40
Ready-to-eat cereal, vitamin D–fortified a 40

a More heavily fortified food products contain greater amounts of vitamin D.

Calcium

Less than half of US women meet the recommendation for dietary intake of calcium. The recommended daily intake of calcium for women 19 to 39 years of age (whether pregnant or not) is 1000 mg/day. For women younger than 18 years of age, 1300 mg/day is recommended. Calcium-rich foods and amounts per serving are shown in Box 12.3 . For optimal benefit, calcium should be taken with adequate dosages of vitamin D and magnesium. A recent review suggested that calcium supplementation may reduce the risk of hypertensive disorders of pregnancy among women with low baseline calcium intake. Women at high risk for preeclampsia may also benefit from calcium supplementation; however, existing studies are limited by heterogeneous populations and small sample size. A Cochrane review published in 2015 concluded that calcium supplementation does not reduce the risk of spontaneous preterm birth.

Box 12.3
Calcium-Rich Foods a

a Recommended Dietary Allowance 1300 mg for individuals 14–18 years old and 1000 mg for individuals 19 years old and older .

Modified from US Department of Agriculture, Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Release 28, 2016. https://ndb.nal.usda.gov/ndb/ .

  • 300–400 mg calcium per serving

    • Yogurt or milk, 8 oz

    • Cheese, 1.5 oz

    • Calcium-fortified soy milk, 8 oz

    • Sardines, canned in oil with bones, 3 oz

  • 150–299 mg calcium per serving

    • Calcium-fortified orange juice, 6 oz

    • Tofu, calcium-fortified, ½ cup

    • Cottage cheese, 1 cup

    • Salmon, canned with bones, 3 oz

  • 10–1000 mg calcium per serving

    • Ready-to-eat cereals, calcium-fortified, 1 cup

  • 50–149 mg calcium per serving

    • Kale, broccoli, bok choi (Chinese cabbage), cooked, 1 cup

    • Ice cream or frozen yogurt, ½ cup

    • Bread, 1 slice

Iron

Iron is critical for fetal development and necessary to expand maternal red cell mass during pregnancy. Pregnant women are among the groups at highest risk of anemia, and iron deficiency is the most common nutritional cause. Epidemiologic data show an association between lower hemoglobin levels and adverse perinatal outcomes, including low birth weight, prematurity, and maternal and infant mortality. Nevertheless, results of clinical trials of iron supplementation to prevent adverse birth outcomes, including trials initiated early in pregnancy, are mixed. Authors of a Cochrane review noted a small (+58 g) increase in birth weight with iron supplementation, but it noted no difference in the incidence of preterm birth, SGA, or low birth weight. Some authors hypothesized that other deficiencies probably accompany iron deficiency and that longer periods of supplementation throughout the reproductive years may be needed to prevent poor birth outcomes.

The National Academy of Medicine recommends an iron intake of 27 mg/day during pregnancy. This amount is included in most prenatal vitamins and thus additional supplementation for nonanemic women is not necessary. Iron is also available in heme and nonheme forms in the diet. Heme iron is found in meat, poultry, and fish. It is the most bioavailable form of iron. Nonheme iron is found in plant foods and supplements and is less bioavailable. Iron supplements are best absorbed when taken with citrus juices, as the vitamin C enhances absorption. Coffee, tea, milk, and calcium supplements inhibit iron absorption and thus should be consumed separately from iron supplements. Box 12.4 shows examples of iron-rich foods and the amounts of iron per serving.

Box 12.4
Iron-Rich Foods a

a Recommended Dietary Allowance 27 mg.

Modified from US Department of Agriculture, Agricultural Research Service. USDA National Nutrient Database for Standard Reference, Release 28, 2016. https://ndb.nal.usda.gov/ndb/ .

  • 18 mg iron per serving

    • Breakfast cereals, fortified with 100% of daily value for iron, 1 serving

  • 5–8 mg iron per serving

    • Oysters, cooked, 3 oz

    • Beef liver, 3 oz

  • 2–4 mg iron per serving

    • Lentils, chickpeas, white beans, or kidney beans, cooked, ½ cup

    • Tofu, ½ cup

    • Green leafy vegetables such as spinach, cooked, ½ cup

    • Tomatoes, canned, stewed, ½ cup

    • Potato, baked, flesh and skin, 1 medium

    • Beef, 3 oz

    • Sardines, 3 oz

    • Cashew nuts, 1 oz (18 nuts)

  • 1 mg iron per serving

    • Green peas, cooked, ½ cup

    • Chicken, turkey, or canned tuna, 3 oz

    • Bread, 1 slice

    • Rice, iron-fortified, cooked, ½ cup

    • Dried fruit (raisins, apricots), ¼ cup

    • Pasta, iron-fortified, cooked, 1 cup

Iodine

Iodine is an element present in food (i.e., fish and dairy products) and added to many table salts. Iodine needs increase during pregnancy, and iodine deficiency can lead to maternal and fetal hypothyroidism and can negatively impact growth and neurocognitive development of the fetus/neonate. The National Academy of Medicine recommends 220 μg of iodine daily during pregnancy.

Choline

Choline is an important source of methyl groups used in many metabolic pathways, and it is transferred efficiently from mother to fetus. Choline needs increase modestly during pregnancy, and pregnant people are at risk for choline deficiency. The National Academy of Medicine recommends 450 mg of choline daily from either food or supplements. Foods high in choline include meat, fish, poultry, and cruciferous vegetables such as broccoli. Many nuts and seeds also contain choline. Importantly, many prenatal vitamins do not contain adequate amounts of choline.

Fish Consumption, Fish Oil Supplements, and Ω-3 Fatty Acids

Fish is a high-protein food that is also the major source of two long-chain polyunsaturated fatty acids: docosahexaenoic acid (DHA) and eicosapentaenoic acid. These ω-3 fatty acids play an important role in fetal and infant brain and retina development and thus are necessary for normal infant visual and cognitive function. Both DHA and eicosapentaenoic acid are also precursors in important inflammatory biologic pathways and have independent antiinflammatory action.

Given the role that ω-3 fatty acids play in both neurodevelopment and inflammatory pathways, fish and fish oil supplementation have been postulated to improve childhood neurologic outcomes as well as inflammatory-mediated diseases, such as spontaneous preterm birth, preeclampsia, allergy, asthma, and eczema. A recent Cochrane review meta-analyzed 70 trials involving 19,927 pregnant people who were randomized to omega-3 long-chain polyunsaturated fatty acid supplements or placebo to evaluate their impact on maternal, perinatal, and neonatal outcomes. They reported that high-quality evidence supported a reduced risk of preterm birth <37 weeks (RR = 0.89; 95% CI, 0.81, 0.97) and preterm birth <34 weeks (RR = 0.58; 95% CI, 0.44, 0.77) with omega-3 supplementation compared with placebo. Some low-quality evidence from 20 trials suggested a beneficial effect of omega-3 supplementation on risk of preeclampsia (RR = 0.84; 95% CI, 0.69, 1.01). The effect of supplementation with small-for-gestational-age birth or fetal growth restriction was null. The remaining associations with child cognition, IQ, neurodevelopment, language, and behavior were null but came from studies the authors deemed low quality.

Given the health benefits of fish intake on preterm birth, both the US Food and Drug Administration (FDA) and ACOG recommend that pregnant women and women who want to become pregnant consume 8 to 12 oz of fish each week. For women who do not eat an adequate amount of fish, fish oils contain the ω-3 fatty acid DHA. In contrast to dietary fish, supplements can be prepared to minimize mercury and other toxin contamination (see later discussion). On the basis of available data, some health authorities recommend that pregnant women aim for an intake of at least 200 mg/day of DHA, either from fish consumption or from marine oil supplements. The study that demonstrated a reduction in the risk of persistent wheeze and asthma with fish oil–derived fatty acid supplementation after 24 weeks used 2.4 g of fish oil.

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