Nutrition in pregnancy: Assessment and counseling

INTRODUCTION — A healthy dietary pattern during pregnancy promotes fetal growth and development and has been associated with lower risks of pregnancy complications, while unhealthy dietary patterns, undernutrition, and overnutrition have been associated with adverse pregnancy outcomes [1-7]. Thus, it is important to evaluate and monitor maternal nutrition both before and during pregnancy, and when appropriate, make changes to improve maternal nutrition.

Many pregnant individuals in the United States have suboptimal diet quality, which began preconception, and most do not meet dietary recommendations [7]. This is especially true among groups at elevated risk for adverse pregnancy outcomes [8]. National Health and Nutrition Examination Survey (NHANES) data indicate that, on average, pregnant or lactating people consume half the recommended amount of total vegetables and dairy products [9]. In a study of 7511 geographically diverse pregnant people in the United States, the top three sources of calories (energy intake) were soda, pasta dishes, and desserts such as cookies and cakes, which are high in added sugars and unhealthy fats [10]. Furthermore, intake of whole grains, dairy products, and healthy fats was especially low, and people with less education or in minority racial and ethnic groups had lower diet quality.

This topic will discuss assessment of maternal diet and maternal counseling about dietary issues during pregnancy, primarily for pregnant people living in middle- and high-income countries; preconception counseling and basic nutritional requirements in pregnancy in this population are reviewed separately. Issues related to pregnant people who reside in resource-limited areas and experience undernutrition are also reviewed separately.

●(See "The preconception office visit", section on 'Core interventions'.)

●(See "Nutrition in pregnancy: Dietary requirements and supplements".)

●(See "Undernutrition in pregnancy: Evaluation, management, and outcome in resource-limited areas".)

ASSESSMENT OF NUTRITIONAL STATUS — Ideally, nutritional status is initially assessed before pregnancy so dietary changes to optimize maternal and child health can begin well before conception [11]. Nutritional assessment and counseling should continue across pregnancy and during lactation. Where available, these activities are best performed using a team approach, which may include the obstetric provider, health professionals trained in prenatal nutrition counseling and education, and a registered dietitian with perinatal nutritional expertise. (See "Dietary assessment in adults".)

History

●Medical and surgical – The medical history can help identify behaviors and medical conditions that pose nutrition-related health risks for the mother and fetus and thus need to be addressed (table 1). For example, use of cigarettes, alcohol, or illicit drugs poses direct health risks but may also affect intake of an adequate and balanced diet: Cigarettes, alcohol, and opioids may suppress appetite while stimulants may increase energy requirements. Some individuals even forget to disclose that they had bariatric surgery, especially if it was laparoscopic and in the distant past. Sequelae of bariatric surgery (eg, micronutrient deficiencies, dumping syndrome) can affect pregnancy management and outcome. (See "Fertility and pregnancy after bariatric surgery".)

●Obstetric – The past obstetric history can impact recommendations for nutrition or supplements before or during future pregnancies. As an example, a past history of a neural tube defect (NTD) in offspring would prompt advice to consume a higher dose of supplemental folic acid (4 mg rather than 0.4 mg) prior to conception and in early pregnancy to reduce the risk of recurrence. (See "Folic acid supplementation in pregnancy", section on 'Either parent with a personal history of NTD or a previously affected offspring'.)

●Dietary – Asking the patient to complete a self-administered questionnaire is helpful for reviewing their typical diet and identifying obvious deficiencies (form 1) [12]. It is important to follow up with specific questions about responses that suggest a possible nutritional issue. Examples of potential problems include skipping meals; limiting food intake; adhering to a self-selected diet; consuming sweetened beverages (eg, soda, sweet tea, sports drinks, energy drinks); low intake of calcium-rich foods, vegetables, or fruits; and high intake of ultra-processed foods with added sugars/fats.

A brief screening questionnaire may be more user-friendly for health professionals in busy practices who are not specifically trained in nutrition (table 2) [12]. This questionnaire has been adapted to assess healthy eating in pregnant people and provides simple tips to improve diet quality. Although this version of the questionnaire has not been validated, a more general version has been validated for assessing diet-related chronic disease risk and has been used successfully in pregnant people [12,13].

Individuals who routinely consume three meals daily that include several servings of vegetables (a variety of green, red/orange, and starchy vegetables), legumes (eg, peas, lentils, beans), fruits, whole grains, low-fat dairy products, and a few sources of protein (eg, meat, poultry, eggs, seafood, nuts, seeds, soy products) likely meet the Daily Recommended Intakes for most nutrients (table 3). However, even nutrient-dense food choices and diets, such as those in the United States Department of Agriculture (USDA) food patterns, may not meet nutrient goals for folate, iron, iodine, vitamin D, and choline during pregnancy [9,14,15]. In a prospective study including approximately 8000 nulliparous participants at eight US medical centers, fewer than one-quarter of the sample consumed a diet that met recommendations for vegetables, fruits, grains, dairy, or protein foods during pregnancy [16].

Physical examination

●Body mass index – The physical examination centers on measurements of height and weight to calculate the body mass index (BMI) and assess whether the individual is at a healthy weight (calculator 1). The patient should be asked what they weighed at their last menstrual period (prepregnancy weight) and this weight should be used for baseline calculations. A prepregnancy BMI of 18.5 to 24.9 kg/m² is normal for White, Hispanic, and Black individuals; for Asian individuals, an upper limit of normal is BMI <23 kg/m² because in this population, higher body fat and higher health risks (especially type 2 diabetes) exist at lower BMIs compared with other populations [17,18]. BMI tables of appropriate pregnancy-related changes in BMI do not exist.

●Signs of a medical disorder or nutritional deficiency – The remainder of the physical examination should screen for signs of nutritional deficiency or a medical disorder. As an example, an eating disorder may cause enlarged parotid glands, eroded tooth enamel, dry skin, and/or hair loss. (See "Eating disorders: Overview of epidemiology, clinical features, and diagnosis".)

Physical signs of gross vitamin deficiency are still observed in areas of the world where diets are very poor due to lack of food. In resource-abundant countries, they occur in special populations, such as individuals with alcohol use disorder, malabsorption, inborn errors of metabolism, and sometimes in those undergoing hemodialysis or receiving parenteral nutrition. (See "Dietary assessment in adults".)

Laboratory

●Hemoglobin/hematocrit is routinely checked at the first prenatal visit and in the late second/early third trimester to assess for anemia; some providers also routinely check the ferritin level to assess for iron deficiency in the absence of anemia. (See "Anemia in pregnancy", section on 'Screening during pregnancy' and "Anemia in pregnancy", section on 'Evaluation of anemia' and "Anemia in pregnancy", section on 'Management'.)

●Although poor vitamin D status in the perinatal period may have short-term or long-term consequences on bone, the immune system, and general health, the precise threshold defining optimal vitamin D status during pregnancy is not well defined. Most experts agree that it is not necessary to perform broad-based screening of serum 25-hydroxyvitamin D levels in the general population or during pregnancy [19,20]. Measurement is reasonable in pregnant people with obesity, those who have minimal sun exposure of skin, have a history of malabsorption (celiac disease, inflammatory bowel disease), or other risk factors for vitamin D deficiency (eg, live at northern latitudes, consume a vegan diet, have dark skin color). (See "Vitamin D deficiency in adults: Definition, clinical manifestations, and treatment".)

INDICATIONS FOR REFERRAL TO A NUTRITION PROFESSIONAL — Referral to a nutrition professional, such as a registered dietitian, with special training in maternal nutrition is recommended for patients with special nutritional considerations [4,21,22]. Registered dietitians who specialize in maternal nutrition can be found online at Academy for Nutrition and Dietetics website by entering the patient's or provider's zip code, selecting "Search by Expertise" and selecting "Maternal Nutrition" under the Expertise Area; however, the list is not comprehensive. For pregnant individuals who qualify for the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC), nutrition counseling and education should be available at WIC appointments. Participation in WIC has been associated with improved birth and pediatric outcomes [23].

Potential indications for referral include:

●Food insecurity or inadequate resources. Individuals with financial constraints regarding the purchase, storage (eg, refrigerator), or preparation (eg, stove) of adequate amounts of appropriate foods require assistance from sources such as the Special Supplemental Food Program for Women, Infants, and Children (WIC) or a social service agency. A short survey form to screen for food insecurity is available from the US Food and Drug Administration (FDA).

●Diabetes, hypertension, inborn metabolic disorders (eg, phenylketonuria, maple syrup urine disease), gastrointestinal disorders that cause malabsorption (eg, Crohn disease, ulcerative colitis, cystic fibrosis), and other disorders that respond to dietary therapy.

●Hyperemesis gravidarum. (See "Hyperthyroidism during pregnancy: Clinical manifestations, diagnosis, and causes" and "Nausea and vomiting of pregnancy: Treatment and outcome".)

●History of bariatric surgery or other gastrointestinal surgery affecting absorption. (See "Fertility and pregnancy after bariatric surgery".)

●Body mass index (BMI) in the overweight or obese range before pregnancy, as over 50 percent of these individuals have been reported to have excessive gestational weight gain [24]. Those with a normal prepregnancy BMI who have inadequate or excessive gestational weight gain (table 4) may benefit from nutritional counseling during pregnancy, as well.

●Unhealthy dietary patterns, such as high intake of sweetened beverages or foods with a high level of calories from added sugars or fats (especially solid fats) and/or low intake of calcium-containing foods, vegetables (aside from corn and potatoes), and/or fruits.

●Inappropriate food consumption patterns, such as food avoidances, self-selected restrictive diets, skipping meals, as these practices may lead to nutritional deficiencies and inadequate gestational weight gain. (See 'Counseling' below.)

●Eating disorders, which may become aggravated by pregnancy or lead to pregnancy complications. (See "Eating disorders in pregnancy".)

●Multiple gestation, which increases nutrient requirements and gestational weight gain targets. (See 'Multiple gestation' below.)

●Use of substances that may affect nutrition (eg, cigarettes, alcohol, illicit drugs, appetite suppressants or stimulants).

COUNSELING

Nutrition counseling and intervention during pregnancy — Pregnancy is a key opportunity for health care professionals to assess nutrition and provide information and tools to help patients consume a healthy diet, which has both short- and long-term benefits for the mother and child. Pregnancy is considered a "window of opportunity" during which individuals are motivated to make healthy changes. It is also a period of frequent interactions with health professionals. Thus, it is important for health professionals to recognize their role and importance in helping mothers make healthy dietary or lifestyle changes. Dietary and physical activity interventions have been successful at improving outcomes, including reducing excessive gestational weight gain, development of gestational diabetes, and the odds of cesarean birth [25].

The American College of Obstetricians and Gynecologists (ACOG) endorses counseling at the initial prenatal visit "regarding benefits of appropriate weight gain, nutrition, and exercise" [26]. In a systematic review of 25 studies in resource-abundant countries, pregnant people who received nutrition information from their health care professionals were more likely to follow recommendations that were specific, clearly explained, and repeated at subsequent prenatal visits [27]. Unfortunately, prenatal nutrition counseling is often not provided, resulting in a missed opportunity [27-29]. Many barriers exist, including a lack of time, resources, and training to provide prenatal nutrition education.

Group prenatal care (eg, CenteringPregnancy) is one potential approach to provide nutrition education to more mothers during pregnancy. This model allows for more time with providers with different expertise, including nutrition professionals. One study of group prenatal care in Iran that included a nutrition module reported the individuals receiving group care were significantly more likely to take vitamin and iron supplements during pregnancy [30]. This is consistent with earlier studies reporting that the group prenatal care model improved multiple outcomes, including increased prenatal knowledge [31]. However, more recent systematic reviews have reported limited evidence on the use of group prenatal care for nutrition-related issues, possibly due to lack of rigor in design [32,33]. (See "Group prenatal care".)

General principles of a healthy diet during pregnancy — Pregnant individuals require higher intakes of many micronutrients and macronutrients (see "Nutrition in pregnancy: Dietary requirements and supplements"). To meet increased requirements, the amount consumed from each food group should increase slightly as recommended by the Dietary Guidelines for Americans (table 5) [9]. The exact amount of foods needed from each food group depends on the amount of calories an individual requires.

Energy (calorie) requirements — Energy needs change across the course of pregnancy, with no increase in calories in the first trimester and slight (+340 kcal/day) and moderate (+452 kcal/day) increases in the second and third trimesters, respectively. Energy needs also vary depending on the individual's prepregnancy body mass index (BMI), age, and physical activity level. Typical caloric needs during pregnancy range from 2200 to 2900 kcal/day in the second or third trimester for individuals with prepregnancy BMIs in the normal range (See "Nutrition in pregnancy: Dietary requirements and supplements", section on 'Energy intake'.).

Calorie needs for a pregnant individual can be estimated using an online calculator. Additionally, MyPlate.gov can provide individually tailored calorie estimates and food group requirements. For individuals with overweight, obesity, or other medical conditions that may affect energy needs, referral to a nutrition professional can be helpful. (See 'Indications for referral to a nutrition professional' above.)

Healthy dietary patterns

Overview — To meet the higher nutrient requirements in pregnancy without exceeding caloric needs, pregnant individuals should choose foods that are nutrient-dense (ie, foods that contain high levels of important nutrients compared with the amount of calories, such as fruits and vegetables, legumes, whole grains, nuts/nut butters, unsweetened yogurt, fish, lean meat) and avoid foods that provide little nutritional value beyond calories: processed foods that are high in added sugars (eg, soda, sweet tea, sweets, desserts, flavored yogurt), added fats (eg, fried foods), and solid fats (eg, high-fat and processed meat). (see "Healthy diet in adults", section on 'Dietary components associated with health benefits') Use of a nutrition screening tool can help health professionals identify pregnant people who may be at risk for lower-quality diets. (See 'History' above.)

The table provides the amounts recommended from each food group for a healthy US-style dietary pattern for pregnant individuals based on calorie needs (table 5) [9]. Generally, the increase in nutrient needs during pregnancy should comprise slight increases in each of the food groups. For people who were underweight prior to becoming pregnant, consultation with a nutrition professional may be necessary to develop appropriate, feasible, individualized strategies to consume adequate nutrients.

Additional resources are available online:

●MyPlate.gov has customizable plans that allow pregnant individuals to obtain personalized recommendations for dietary patterns.

●Tips for Pregnant Moms from the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) is available in both English and Spanish.

●The Food and Information Center of the United States Department of Agriculture (USDA), which provides several online resources for pregnant people, including information on folic acid, food safety, foods to avoid, and nutrition.

Mediterranean diet — A Mediterranean dietary pattern is a way of eating based on the traditional cuisines of countries that border the Mediterranean Sea, such as Greece and Italy. It focuses on plant-based foods, including whole grains, vegetables, fruits, beans, nuts, and seeds, and is higher in fish and olive oil [34]. Dairy and poultry are included in moderation, while red meats and sweets are consumed infrequently.

In nonpregnant adults, this type of dietary pattern has been associated with reduced risks for cardiovascular disease, stroke and cancer, and with improved glycemic control and cognitive function [35-39]. It is notable that many of the studies are observational and thus may be limited by confounding. Research examining the Mediterranean diet during pregnancy, which also tends to be observational, has suggested that this dietary pattern is associated with a reduction in gestational diabetes and hypertensive disorders of pregnancy [40,41] and may have favorable effects on offspring, such as possible reductions in wheeze in early childhood and lower waist circumference, but no effect on preterm birth, obesity, or asthma [42,43]. However, data are limited and most of the research was conducted among healthy White females with access to health care, resulting in limited generalizability.

Issues regarding self-imposed dietary restraints — Self-imposed dietary restraints, such as those described in the following sections, can be problematic if essential nutrients are left out of the diet or weight gain is inadequate.

Vegetarian-type diets — Vegetarian diets vary according to the degree of avoidance of foods of animal origin [44]. The nutritional adequacy of a vegetarian diet must be judged individually, based on the type, amount, and variety of nutrients that are consumed [45]. Healthy vegetarian dietary patterns include the same amount of vegetables, fruits, and dairy as a healthy US-style dietary pattern (table 5). To account for the lack of meats, poultry, and seafood, the amount of grains should increase by 0.5 cup per day, with larger increases in the amounts of vegetarian protein sources: nuts and seeds, soy products, beans/peas/lentils, and eggs [9].

Vegetarian diets are frequently grouped as follows (ordered from less restricted to more restricted), and potential deficiencies are described:

●Semivegetarian – People who occasionally consume meat, fish, or chicken in their diet. Some people who follow such a diet may not eat red meat but may eat fish and perhaps chicken.

In some Asian cultures, animal protein sources may be consumed only once or twice a week. Although these individuals would not label themselves as vegetarian, in American research studies they would be categorized as semivegetarian, as animal protein intake in the United States tends to be significantly higher than once or twice a week.

●Pescatarian – Vegetarians whose diet includes fish on occasion in addition to eggs, milk, and milk products, but no other animal meats. Adequate nutrient consumption is possible.

●Lacto-ovo-vegetarian – Eggs, milk, and milk products (lacto = dairy; ovo = eggs) are included, but no meat is consumed. Adequate consumption of most nutrients is possible. Possible inadequate intake of omega-3 (also called n-3) fatty acids.

●Lactovegetarian – Milk and milk products are included in the diet, but no eggs or meat are consumed. Possible inadequate intake of choline and omega-3 fatty acids. Likely inadequate intake of iron.

●Macrobiotic – Whole grains, especially brown rice, are emphasized, and vegetables, fruits, legumes, and seaweeds are included in the diet. Locally-grown fruits are recommended. Animal foods limited to white meat or white-meat fish may be included in the diet once or twice a week. Likely inadequate intake of vitamin B12, choline, iron, calcium, and omega-3 fatty acids.

●Vegan – All animal products, including eggs, milk, and milk products, are excluded from the diet. Some vegans do not use honey. They also may avoid foods that are processed or not organically grown [46]. Likely inadequate intake of vitamin B12, choline, iron, calcium, and omega-3 fatty acids.

●Fruitarian – Vegan diet based on fruits, nuts, and seeds. Vegetables classified botanically as fruits (avocado, tomatoes) are commonly included in fruitarian diets; all other vegetables, grains, beans, and animal products are excluded. Likely inadequate intake of multiple micronutrients and possibly protein.

Issues in pregnancy — Although well-planned vegetarian and vegan diets are generally considered safe during pregnancy and lactation, high-quality data are sparse [47-49]. Attention to appropriate intake of key nutrients is essential. Consuming a vegetarian diet does not equate with healthy, as vegetarian diets may include processed foods high in sugar and fat, similar to the diet of omnivores; therefore, individual nutritional assessment of the pregnant person's vegetarian diet with a registered dietitian is advisable [49-52].

Potential concerns include:

●Low birth weight/small for gestational age – Some studies have reported lower birth weight and small for gestational age offspring of pregnant individuals consuming a vegetarian or vegan diet [53,54].

●Inadequate micronutrient intake – Well-balanced vegetarian diets are similar to well-balanced omnivore diets in that they meet most nutrient goals, with the likely exceptions of iron, vitamin D, vitamin E, and choline for some types of vegetarian diet [15,55] (see 'Vegetarian-type diets' above). Additional potential nutrients of concern, particularly for vegans and diets that completely avoid animal source foods, are calcium, vitamin B12, and omega-3 fatty acids (eicosapentaenoic acid and docosahexaenoic acid) [47,48,56]. In one review, pregnant people on a vegan diet were at higher risk for both iron and vitamin B12 deficiencies [48].

Micronutrient deficiencies can often be resolved with minor dietary alterations or supplements. For example, fortified vegetarian/vegan food products are now widely available and include some nondairy milks (such as fortified soy beverages), calcium-fortified orange juice, meat substitutes (eg, tofu, tempeh), and fortified breakfast cereals. These products can be good sources of key nutrients, such as calcium, iron, zinc, vitamin B12, vitamin D, riboflavin, and omega-3 fatty acids. Of note, some natural food brands are not enriched or fortified to the same degree as mainstream products.

If all animal source foods are excluded and dietary modifications are not possible or unlikely, use of one or more of the following supplements needs to be considered:

•Vitamin B12

•Omega-3 fatty acids (eg, vegan algae-based supplements [spirulina and chlorella])

•Choline

•Iron

•Vitamin D

•Vitamin E

•Calcium

Vitamin D, E, and iron are generally provided in sufficient amounts by a standard prenatal vitamin. Other nutrients should be evaluated and provided individually as needed. (See "Nutrition in pregnancy: Dietary requirements and supplements".)

●Inadequate macronutrient intake – Limited research in populations outside of the United States showed that the macronutrient intake of pregnant vegetarians was similar to that of pregnant nonvegetarians except the pregnant vegetarians consumed statistically less protein and more carbohydrates; however, none of the studies reported protein deficiency in pregnant vegetarians [57,58]. Protein quality in well-balanced vegetarian diets need not be a concern as long as total energy intake is adequate (because it provides a protein-sparing effect).

Although individual plant sources of protein tend to be incomplete in their provision of all essential amino acids, eating a variety of types of plant protein sources (grains, legumes, nuts) over the course of a day can provide all essential amino acids [59].

●Effect of phytoestrogens – Phytoestrogen consumption tends to be higher among vegetarians than among omnivores. Although concerns have been raised regarding phytoestrogen intake and reproductive development (hypospadias [60]), subsequent research found no correlation [61]. Available evidence does not support an association between vegetarian diets and risk of disrupted reproductive development. (See "Endocrine-disrupting chemicals".)

Gluten-free diet — Gluten-free grains often do not contain the same levels of added folate, calcium, and iron compared with wheat products; therefore, elimination of gluten-rich foods during pregnancy could result in inadequate intakes of these nutrients as well as thiamin, riboflavin, and niacin. However, use of other whole grain foods (eg, quinoa, brown rice, buckwheat, gluten-free oats, plus amaranth or sorghum for iron), in addition to standard folic acid supplementation of 400 to 800 mcg/day, should prevent any nutritional deficiency and these diets are generally considered safe. (See "Nutrition in pregnancy: Dietary requirements and supplements".)

●Patients with celiac disease – Patients with celiac disease benefit from following a gluten-free diet. In systematic reviews of case-control and cohort studies, females with untreated celiac disease were at increased risk of reproductive failure compared with females in the general population and treatment with a gluten-free diet eliminated the excess risk of complications [62-64]. (See "Epidemiology, pathogenesis, and clinical manifestations of celiac disease in adults", section on 'Menstrual and reproductive issues'.)

●Patients without celiac disease – Gluten-free diets are now also popular in the general population and are promoted in the lay press as having health benefits despite a lack of evidence to support this claim in patients without celiac disease or gluten sensitivity [65,66]. While there is no evidence to support their use in the absence of celiac disease or documented gluten sensitivity, gluten-free diets can provide adequate nutrition.

Low-carbohydrate diet — The recommended minimum carbohydrate requirements for nonpregnant and pregnant females is to consume a minimum of 130 and 175 grams per day, respectively [9,67]. Nonpregnant individuals may choose to follow a low-carbohydrate diet for a variety of reasons, in particular management of type 2 diabetes and weight loss [68].

"Low-carb" diets vary greatly in the amount of carbohydrates consumed. Technically, any diet that provides less than 45 percent of energy from carbohydrates may be considered "low carb." For a 2000 calorie diet, this would be less than 225 grams per day. However, low-carb diets may limit carbohydrate intake to as little as 50 grams per day (see 'Ketogenic diet' below). Pregnant patients should consult with a health professional before restricting carbohydrates below the daily recommended intake of 175 grams per day and we recommend avoiding extremely low-carbohydrate diets during pregnancy. Moderate carbohydrate restriction may be acceptable, particularly in patients with gestational diabetes, but this should take place under the care of a health professional trained in management of gestational diabetes.

●Possible relationship with neural tube defects – In a review of data from the National Birth Defects Prevention Study, pregnant people with restricted carbohydrate intake had less than half the folate intake of pregnant people with nonrestricted carbohydrate intake and also appeared to be at slightly increased risk of having an infant with a neural tube defect (NTD; odds ratio 1.30, 95% CI 1.02-1.67) [69]. A subsequent study using prefolic acid food fortification data also noted this association between low-carbohydrate diets and NTDs, suggesting that the increased risk may not be related solely to low folic acid intake in the postfortification era [70]. Although a causal role between restricted carbohydrate intake (≤5^th percentile or 95 g/day) and NTDs has not been established, for females who follow low-carbohydrate diets, it is prudent to emphasize the importance of the standard recommendation that all reproductive-age females take a 0.4 to 0.8 mg folic acid supplement one month before and for the first two to three months after conception. Further investigation between low-carbohydrate diets and NTDs is needed. (See "Nutrition in pregnancy: Dietary requirements and supplements", section on 'Folate/folic acid'.)

Ketogenic diet — The ketogenic diet is one type of very low-carbohydrate diet, classically consisting of high-fat, moderate-protein, and extremely low-carbohydrate consumption that produces metabolic changes associated with the starvation state. These diets were initially developed to treat seizure disorders, but have since been promoted for weight loss and other health reasons, and can be either hypocaloric or normocaloric [71]. Ketogenic diets typically restrict carbohydrate consumption to 5 to 10 percent of energy needs, which would provide only 25 to 50 grams per day of carbohydrate. (See 'Low-carbohydrate diet' above.)

There is minimal information on the fetal effects of the ketogenic diet in human pregnancy [72,73], which is concerning since maternal changes in plasma ketones, insulin, glucose, glucagon, and free fatty acids can be quite profound. Rodent studies have reported potentially adverse fetal effects, such as fetal overgrowth, and changes in organ (heart) size and brain structures [74,75]. Furthermore, rodent mothers fed a ketogenic diet exhibited reduction in fertility, litter size, and high risk of fatal ketoacidosis during lactation [76]. Given these animal data, a lack of evidence of the effects in humans, and concerns about a very low-carbohydrate diet in the absence of folic acid supplementation, we and others recommend avoiding ketogenic diets during pregnancy [7].

Paleolithic diet — The "Paleo" diet was developed based on an idea that foods from the paleolithic era, a hunter-gatherer period prior to farming and cultivation, may promote greater health. This diet generally includes nuts, fish, meat, eggs, and some fruits and vegetables and excludes dairy, grain-based foods, legumes, refined sugar, table salt, and processed foods [77]. It tends to be high in protein, moderate in fat (mainly unsaturated fats), low to moderate in carbohydrates, and low in sodium. It may be low in folate, certain types of fiber, and calcium due to the exclusion of grains, legumes, and dairy [78,79]. One study among nonpregnant females reported a rise in iodine deficiency after six months of consuming a Paleo diet [80].

There is limited research about the Paleo diet in pregnant people. In one retrospective cohort study comparing 37 pregnant people with low-risk pregnancies who adhered to this diet before and throughout gestation with 39 similar low-risk pregnant people who consumed a regular diet, the Paleo diet was associated with lower glucose challenge test results (one hour glucose level: 95.8 versus 123.1 mg/dL), higher hemoglobin levels (12.10 versus 11.05 g/dL) and ferritin (32.1 versus 21.3 mg/mL), lower gestational weight gain (9.3 versus 10.8 kg), and lower birth weight (3098 versus 3275 g), with no differences in adverse neonatal outcomes [81].

A Paleo diet during pregnancy may be acceptable, as it includes vegetables, fruits, and healthy proteins, while also excluding or limiting added sugars, certain processed foods, and processed meats. However, it is likely to provide insufficient amounts of key nutrients.

For pregnant people on Paleo diets, we suggest a prenatal vitamin containing at least 400 to 800 micrograms of folic acid and 150 to 250 micrograms of iodine (if they do not consume iodized table salt) and calcium supplements of 1000 mg divided into two or three doses throughout the day. Some authors have advised against the Paleo diet because of the dairy restriction [7]. (See "Nutrition in pregnancy: Dietary requirements and supplements", section on 'Micronutrients'.)

Intermittent fasting — Intermittent fasting may involve fasting for several hours during the day or for one or more days. Fasting may occur for religious reasons or to promote weight loss [82]. The effects of intermittent fasting in otherwise healthy pregnant people are not well defined. Some authors have hypothesized that prolonged daytime fasting during pregnancy, such as during Ramadan (see 'Ramadan fasting' below), can lead to permanent epigenetic alterations in fetal physiology (fetal programming) that have adverse consequences in adult life [82]. In ovine and human studies, the most consistently reported effect of daytime fasting is reduction in fetal breathing movements, with resolution in the fed state [83-87]. There is no information on the effect of ketonuria on fetal/neonatal outcome in the absence of ketoacidosis.

Nighttime fasting is better understood. During an overnight 12- to 18-hour fast, plasma glucose, insulin, and alanine levels fall, and plasma-free fatty acids and beta-hydroxybutyrate levels rise, a phenomenon termed "accelerated starvation" [88]. With early conversion to fat metabolism, other fuels, such as glucose and amino acids, are more available for the fetus. Free fatty acids and beta-hydroxybutyrate are also transferred across the placenta and metabolized by the fetus.

Ramadan fasting — A meta-analysis of 22 studies of short-term pregnancy outcome in nearly 19,000 pregnancies exposed to Ramadan fasting (during which fasting occurs from sunrise to sunset) observed no adverse effects on birth weight or preterm birth rate, but a reduction in placental weight in one of the three studies that reported this outcome [89]. Rare outcomes such as stillbirth and neonatal death could not be assessed. However, a longer-term study reported that exposure to Ramadan in early pregnancy may have adverse effects on childhood mortality [90]. In this study of 20 years of data from Burkina Faso, when Ramadan occurred during conception, the first trimester, or the second trimester, the under-age-five mortality rates of children born to Muslim mothers were 33, 29, and 22 percent higher, respectively, than in children of non-Muslim mothers born at the same time. Childhood mortality in offspring of Muslim mothers was not increased with exposure during the third trimester or in the absence of in utero exposure. However, it should be noted that most of the population of Burkina Faso lives by subsistence farming and has seasonal food insecurity and the pregnant people may have been nutritionally deprived in addition to fasting; many young children are chronically nutritionally deprived. Thus, the findings in this study may not apply to Muslim females in other countries where food insecurity is not prevalent. Other lifestyle changes also occur during Ramadan, such as increases in fat and sugar consumption, which may also play a role in the observed association.

Additional studies are needed to determine the effects of factors such as the trimester of pregnancy when Ramadan fasting occurs, coexistence of medical conditions and pregnancy complications, and the geographic location of the population. Information on the long-term development of offspring would also be useful.

Other dietary issues

Lactose intolerance — Lactose intolerant patients who are unable to consume adequate amounts of calcium through dairy and other dietary components can take calcium supplements or consume calcium-fortified foods and beverages, such as fortified soy beverages. There are no data on the safety of commercially available "lactase" preparations during pregnancy; however, beta-galactosidases are normal constituents of human tissues. (See "Lactose intolerance and malabsorption: Clinical manifestations, diagnosis, and management".)

Of note, pregnant people with lactose maldigestion have improved lactose tolerance in late pregnancy [91,92]. This has been attributed to slower intestinal transit during pregnancy and bacterial adaptation to increased lactose intake.

Food avoidance/consumption to prevent atopic disease in offspring — Both avoidance and ingestion of specific antigens, such as peanuts, milk, and eggs, during pregnancy have been hypothesized to reduce the frequency of atopic disease in offspring, but the bulk of evidence does not support either approach and early postnatal exposure may be the modifiable determinant. These diets are not recommended. (See "Primary prevention of allergic disease: Maternal diet in pregnancy and lactation".)

On the other hand, breastfeeding may reduce the risk of allergic disease in offspring and is recommended. (See "The impact of breastfeeding on the development of allergic disease".)

Consumption of nonfluoridated bottled or tap water — Theoretically, pregnant people who live in areas where water is not fluoridated or who only consume bottled water not containing fluoride may not achieve adequate intake of fluoride, which is 3 mg/day in nonpregnant, pregnant, and breastfeeding people [93,94]. Fluoride intake is difficult to determine, given that fluoride may be present in liquids used for bottled beverages and prepared foods (eg, soups, canned vegetables) and is present in tea and seafood that contains edible bones or shells.

The United States Centers for Disease Control and Prevention (CDC) recommends not supplementing fluoride during pregnancy [95] because prenatal fluoride supplementation is not incorporated into primary teeth [96] and did not reduce caries in offspring in the only randomized trial of this intervention [97,98]. The benefits of fluoride occur almost entirely after tooth eruption as a direct topical effect on teeth; earlier hypotheses that ingested fluoride is systemically incorporated into developing tooth enamel have been largely discredited as a primary mechanism of fluoride action [99,100]. On the other hand, there is good evidence that postnatal exposure of newly erupted teeth to topical fluoride from water or dentifrice is efficacious [99,100].

Excessive ingestion of fluoride during pregnancy does not appear to produce fluorosis in offspring [101]. Although fluoride readily crosses the placenta, the placenta may provide a partial barrier to transfer of excess fluoride when maternal levels are high [102]. However, a possible association with neurodevelopmental effects has been reported in ecological studies in China and Mexico and a multicenter birth cohort study in Canada [103-106]. The source of fluoride in the Canadian and Mexican studies was optimally fluoridated water consumed as tap water and other water-based beverages. The Canadian study also adjusted for tea consumption, which has a high-fluoride content. The source of fluoride in the Chinese study was well water; there was no adjustment for tea consumption. The observed association may be related to bias, imprecision, and unmeasured confounding; further investigation is warranted before fluoride can be considered a neurodevelopmental toxicant [107]. (See "Overview of dietary trace elements" and "Preventive dental care and counseling for infants and young children".)

Use of non-nutritive sweeteners — The US Food and Drug Administration (FDA), which regulates nutritive and non-nutritive sweeteners in the United States, has deemed acesulfame potassium (eg, Sunett, Sweet One), advantame, aspartame (eg, NutraSweet, Equal), neotame (eg, Newtame), saccharin (eg, Sweet'N Low), luo han guo fruit extract (Siraitia grosvenorii Swingle fruit extract), >95 percent purity steviol glycosides (eg, Stevia, Truvia, SweetLeaf), and sucralose (eg, Splenda) to be safe for use by the general public, including during pregnancy [108]. Saccharin, acesulfame, and sucralose cross the placenta whereas aspartame does not because it is fully digested in the gastrointestinal tract [109].

Intake of non-nutritive sweeteners is common and has increased dramatically among pregnant people in the United States over the last decade [110,111]. Although clinical studies on the short- and long-term effects of consumption of these substances during pregnancy are limited, no data suggest that use of aspartame, sucralose, saccharin, acesulfame potassium, or stevioside by pregnant people increases the risk of congenital anomalies above the baseline risk in the general population [112]. However, other issues, including increased infant BMI, childhood obesity, a small increase in preterm birth, and an altered childhood preference for sweet taste, have been observed, and the effects appear to be independent of overall diet quality, energy intake, or other obesity risk factors [113-119]. Pregnant people with phenylketonuria should avoid aspartame because it is converted into phenylalanine in the body.

We consider consumption of small amounts of non-nutritive sweeteners during pregnancy acceptable, particularly to replace sugar, such as in patients with gestational diabetes where refined sugar consumption can be detrimental. The acceptable daily intake (ADI) is defined as an estimate of the amount of a food additive that can be ingested daily over a lifetime without appreciable health risk. Average use of non-nutritive sweeteners is usually below this limit. For example, the ADI for aspartame is 50 mg/kg/day; Diet Coke contains 131 mg aspartame per 355 mL can and one packet of Equal contains 33 mg of aspartame. The ADI for saccharin and sucralose is 5 mg/kg/day, for acesulfame potassium it is 15 mg/kg/day, and for stevioside it is 4 mg/kg/day.

An overview of issues related to use of non-nutritive sweeteners is available separately. (See "Overview of non-nutritive sweeteners".)

Consumption of sugar-sweetened beverages — Sugar-sweetened beverages include soda, sweet tea, sports drinks, and juices. These drinks tend to be high in calories and low in nutritive value; therefore, more than occasional intake of sugar-sweetened beverages is discouraged in all populations. National Health and Nutrition Examination Survey (NHANES) data indicate that pregnant females in the United States consume an average of 1.3 sugar sweetened beverages per day, with the highest intake among those with incomes below the federal poverty level, a group with other social determinants of poorer health [120].

Concerns have been raised about consumption of these beverages by pregnant people. Consumption can lead to large spikes in blood glucose, which can be particularly problematic during pregnancy, when insulin resistance is naturally increased to promote adequate nutrient availability to the fetus. In addition, sugar-sweetened beverage consumption has been associated with poorer diet quality and extra calories (estimated to be an extra 203 kcal/day), which may contribute to excess gestational weight gain [120]. Maternal sugary beverage intake has also been associated with risk for preeclampsia [121], conflicting findings regarding risk for preterm birth [118,122], and increased adiposity in school-aged children. With respect to offspring, one study reported that for each additional serving of a sugary beverage consumed by a mother during the second trimester, fat mass in offspring increased by 0.15 kg/m² [123]. The association persisted after adjustment for multiple confounding variables and was independent of the offsprings' beverage intake, and no such association was found for maternal intakes of diet soda or water. These findings add to an increasing body of data supporting prenatal programming of susceptibility to obesity.

FOOD SAFETY

Avoidance of foodborne infections — Foodborne illnesses can cause maternal disease as well as congenital disease, miscarriage, preterm labor, and fetal death. To reduce the risk of foodborne illness [124]:

●Practice good personal hygiene (frequent hand washing).

●Consume only meats, fish, and poultry (including eggs) that are fully cooked.

●Avoid deli meats, hot dogs, and smoked seafood. Alternatively, cook them until they steam to destroy bacteria (particularly listeria).

●Avoid unpasteurized dairy products and fruit/vegetable juices.

●Thoroughly rinse fresh fruits and vegetables under running water (approximately 30 seconds) before eating.

●Avoid eating raw sprouts (including alfalfa, clover, radish, and mung bean). Bacteria can get into sprout seeds through cracks in the shell; these bacteria are nearly impossible to wash out.

●Wash hands, food preparation surfaces, cutting boards, dishes, and utensils that come in contact with raw meat, poultry, or fish with hot, soapy water. Countertops can be sanitized by wiping with a solution of one teaspoon liquid chlorine bleach per quart of water and leaving to dry over 10 minutes.

In the United States, FoodSafety.gov provides detailed advice on food safety for people who are pregnant or planning pregnancy.

The following foodborne infections can have adverse effects on pregnancy. These infections and strategies for avoiding them are described in detail separately:

●Toxoplasmosis – Toxoplasmosis is caused by ingestion of undercooked or cured meat or meat products, fruit or vegetables contaminated by infected soil, and contaminated unfiltered water. (See "Toxoplasmosis and pregnancy".)

●Listeriosis – Listeria monocytogenes is a common low-level bacterial contaminant of both processed and unprocessed foods of plant and animal origin; hot cooked foods are not a vehicle for its transmission. L. monocytogenes is most associated with processed/delicatessen meats, hot dogs, soft cheeses, smoked seafood, meat spreads, and pâté, but has also been transmitted by fresh fruits and vegetables that are commonly eaten uncooked. (See "Clinical manifestations and diagnosis of Listeria monocytogenes infection".)

●Brucellosis – Brucellosis is caused by ingestion of contaminated food such as raw milk, cheeses made from unpasteurized (raw) milk, or raw meat. (See "Brucellosis: Epidemiology, microbiology, clinical manifestations, and diagnosis".)

Information about current foodborne illness outbreaks in the United States can be found at the Centers for Disease Control and Prevention website.

Guidelines for safe seafood consumption — Pregnant people are advised to eat only cooked fish to avoid potentially harmful organisms [125]. However, pregnant people who have consumed "sushi grade" raw fish can be reassured that this is generally safe [126], as long as the raw fish was frozen appropriately [127], as this eliminates most parasites and bacteria. These individuals should be advised to discontinue future raw fish consumption. A variety of marine toxins (eg, ciguatoxin) can be ingested via fish consumption (cooked or raw), but there are only rare reports of adverse effects on pregnancy or the fetus. (See "Overview of shellfish, pufferfish, and other marine toxin poisoning".)

Fish may be contaminated by environmental pollutants, such as methylmercury. Methylmercury exposure, primarily through ingestion of contaminated fish, can cause severe fetal central nervous system damage, as well as milder intellectual, motor, and psychosocial impairment. For this reason, the FDA and the Environmental Protection Agency (EPA) recommend that pregnant people (or people who might become pregnant or who are nursing) should [125]:

●Avoid eating any shark, swordfish, king mackerel, marlin, orange roughy, tilefish (Gulf of Mexico), or bigeye tuna (other kinds of tuna are acceptable) because they may contain high levels of mercury; an online table of mercury content in commercial fish and shellfish is available.

●Eat two to three servings (8 to 12 oz total) per week of seafood that is likely very low in mercury or other contaminants ("best choices") or one serving of seafood (4 oz) that is likely low in mercury or other contaminants ("good choices"). A chart to help consumers make appropriate choices is available online. Additional information on specific levels of methylmercury and other contaminants is available through the FDA food safety website and the EPA website.

●Check local advisories about the safety of fish caught in local lakes, rivers, and coastal areas.

The risks and benefits of fish consumption and fish oil supplements during pregnancy are reviewed in detail separately. (See "Fish consumption and marine omega-3 fatty acid supplementation in pregnancy".)

Guidelines for safe caffeine intake — Females who are attempting to conceive or who are pregnant are generally advised to limit caffeine consumption to less than 200 to 300 mg per day (table 6). A short list of the caffeine content of beverages and foods is available in the table (table 7); a longer list is available online.

Available data on the safety of any caffeine intake is of low quality. The effect of extraneous variables and possible misclassification of exposure and outcome variables remains a limitation of observational studies. These data and the effects of caffeine on pregnancy outcomes are discussed in detail separately. (See "Caffeine: Effects on reproductive outcomes in females".)

Avoidance of herbal products (except ginger) — Herbal medicines and supplements should generally be avoided during pregnancy [128-130], except for ginger (see "Nausea and vomiting of pregnancy: Treatment and outcome", section on 'Ginger supplements'). The practitioner has no control over the strength or purity of the individual herbs; herbal preparations can interact with commonly prescribed medications and lead to dangerous side effects [131,132]; and several cases of potentially harmful effects to the pregnancy have been reported [130,133-137]. In the United States, makers of supplements are not required to prove efficacy, safety, or quality of a product before it is on the market, and numerous recalls of supplements have taken place due to product adulteration. (See "Overview of herbal medicine and dietary supplements", section on 'Regulation in the United States'.)

Consumption of herbal products is common. In the United States, 5 to 10 percent of pregnant people reported herbal intake during pregnancy [138,139] and 15 percent reported using an herbal product or nonvitamin supplement, most commonly fish oil, melatonin, probiotics or prebiotics, acai, and cranberry [140]. Estimates of herbal intake have been higher in Europe and Australia, as high as 58 percent of pregnant people in one United Kingdom sample [141]. The most common products were herbal teas, chamomile, ginger, cranberry, raspberry leaf, echinacea, and ephedra.

There is a paucity of high-quality randomized trials evaluating the efficacy and safety of traditional herbal preparations in pregnancy [142]. In a 2016 systematic review that examined the effects of herbal medicines on miscarriage, none of nine randomized trials compared herbal medicines with either placebo or bed rest; thus, the authors concluded that there were insufficient data to make recommendations [143]. Some studies have reported lack of positive effects of herbal remedies [144], while others have reported negative effects on pregnancy and infant outcomes (eg, almond oil, licorice, and chamomile have been associated with preterm birth; mwanaphepo has been associated with maternal and neonatal morbidity) [130,137]. One systematic review found that raspberry leaf was associated with cesarean birth, while another concluded that it resulted in neither harm nor benefit [130,145]. A meta-analysis of nine studies found evening primrose oil was associated with a shorter duration of first- and second-stage labor and a reduction in cesarean birth, however, further research was recommended due to the low quality of the studies [146].

Caution regarding consumption of liver-based foods — High consumption of liver or liver-based foods (eg, liver patties or sausage) may be harmful in pregnancy because of excessive intake of vitamin A. Some groups have recommended limiting or avoiding liver consumption in pregnancy for this reason. (See "Nutrition in pregnancy: Dietary requirements and supplements", section on 'Supplements and dietary intake that can be harmful'.)

Limiting exposure to environmental toxins — Reducing exposure to toxic environmental agents is a critical area for intervention because of effects of toxins on the developing fetus [147]. Good nutrition is one way to buffer exposure to toxic agents [148,149]. Pregnant people should be encouraged to eat plenty of fruits and vegetables (either conventional or organic), legumes, and whole grains every day, and to avoid processed foods and fast foods.

●Bisphenol A and phthalates – Food can be a source of exposure to environmental toxins, such as bisphenol A (BPA), phthalates, and pesticides. BPA enters into food and beverages from containers that are made with BPA (eg, lining of canned foods, polycarbonate plastics heated in a microwave oven or dishwasher). Phthalates are used in food production and storage containers (such as conveyer belts, jar lids, tubing, gloves, and packaging) and can seep into a wide variety of foods and beverages during processing and packaging [150]. Exposure is a concern during pregnancy because of potential increase in preterm birth and neural and behavioral effects in offspring.

Pregnant people should be encouraged to avoid use of plastics for food and beverage containers that contain BPA and avoid canned goods that use BPA linings (BPA-free canned goods are increasingly available). (See "Occupational and environmental risks to reproduction in females: Specific exposures and impact", section on 'Bisphenol A and other phenols' and "Overview of occupational and environmental risks to reproduction in females", section on 'Interference with fetal development'.)

●Pesticide and antibiotic residues – The effects of pesticide exposure from foods are unclear. The American Academy of Pediatrics recognizes that early pesticide exposure may adversely impact birth weight, risk of pediatric cancers, and cognitive function and behavior [151]. The EPA sets a maximum residue limit, which is the amount of pesticide residue allowed to remain on each food or product [152]. This limit is set to ensure that "there is reasonable certainty of no harm." Much of the public, however, is still concerned about pesticides in food.

Consumption of organic foods may reduce exposure to pesticide residues and antibiotics (which can promote antibiotic resistant bacteria) [153]. On the other hand, organic foods have not been found to be nutritionally superior and tend to be more expensive and less accessible, particularly for disadvantaged populations. (See "Overview of occupational and environmental risks to reproduction in females", section on 'Interference with fetal development'.)

Tips to help reduce pesticide residues on foods include [154]:

•Eat a variety of fruits and vegetables to minimize exposure to a single pesticide

•Thoroughly wash all produce, even organic produce and produce that is peeled before consumption

•Wash produce under running water rather than dunking or soaking it

•Scrub produce that is firm (eg, melons, root vegetables)

•Dry produce with clean cloth or towel, if possible

•Discard outer layer of lettuce or cabbage

•Trim fat and skin from meat, poultry, and fish to minimize pesticide residues that accumulate in fat

SPECIAL POPULATIONS

Multiple gestation — Nutritional requirements and weight gain recommendations are higher in multiple gestations. Guidelines are provided separately. (See "Twin pregnancy: Routine prenatal care", section on 'Nutrition and supplements' and "Twin pregnancy: Routine prenatal care", section on 'Gestational weight gain' and "Triplet pregnancy", section on 'Weight gain'.)

Pregnant people with diabetes — Medical nutritional therapy for patients with pregestational or gestation diabetes is reviewed separately. (See "Pregestational (preexisting) diabetes mellitus: Antenatal glycemic control", section on 'Medical nutrition therapy' and "Gestational diabetes mellitus: Glucose management and maternal prognosis", section on 'Medical nutritional therapy'.)

Postpartum and breastfeeding — An adequate, balanced diet is important for replenishing maternal stores that are expended during the pregnancy, promoting loss of excess weight, and nourishing the breastfed infant. Maternal nutrition in the postpartum period, including during lactation, is discussed separately. (See "Maternal nutrition during lactation" and "Overview of the postpartum period: Disorders and complications", section on 'Postpartum weight retention'.)

Pregnant people with undernutrition living in resource-limited areas — Pregnant people with potentially severe undernutrition living in resource-limited areas require careful assessment and a different approach to treatment, which is reviewed separately. (See "Undernutrition in pregnancy: Evaluation, management, and outcome in resource-limited areas".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Nutrition and supplements in pregnancy".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Nutrition before and during pregnancy (The Basics)" and "Patient education: Health and nutrition during breastfeeding (The Basics)" and "Patient education: Vegetarian diet (The Basics)")

●Beyond the Basics topic (see "Patient education: Health and nutrition during breastfeeding (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Assessment and referral – Ideally, a female patient's nutritional status is initially assessed before pregnancy so dietary changes to optimize maternal and child health can begin well before conception. Nutritional assessment and counseling should continue across pregnancy and during lactation. Completion of a self-administered dietary questionnaire prior to seeing the clinician can be helpful (form 1 and table 2). (See 'Assessment of nutritional status' above.):

Consultation with a trained specialist in maternal nutrition, such as a registered dietitian, is recommended for pregnant people with high-nutrition risk. Some examples are listed in the table (table 1). (See 'Indications for referral to a nutrition professional' above.)

●Counseling

•Healthy diet – Pregnant people should be counseled to eat a healthy dietary pattern during pregnancy, consistent with the Dietary Guidelines for Americans (table 5). This includes plenty of fruits and vegetables, whole grains, low-fat dairy, and a variety of proteins. Nutrient-dense foods should be encouraged, and empty calories should be minimized or avoided. The exact amount of foods needed from each food group depends on a combination of factors, including the individual's prepregnancy body mass index (BMI), physical activity level, age (adolescent versus adult), and trimester (first versus second and third trimesters). (See 'General principles of a healthy diet during pregnancy' above.)

•Avoiding foodborne infections – Patients should be educated about the risk for and prevention of foodborne infections. (See 'Avoidance of foodborne infections' above.)

•Avoiding potentially toxic foods – Certain foods should be limited or avoided during pregnancy because of potentially toxic effects. These include consumption of fish high in mercury or environmental toxins, high-caffeine intake, unwashed fruits/vegetables, unpasteurized dairy and fruit juices products, herbal products, liver-based foods, and undercooked meats. (See 'Guidelines for safe seafood consumption' above and 'Guidelines for safe caffeine intake' above and 'Avoidance of herbal products (except ginger)' above and 'Caution regarding consumption of liver-based foods' above and 'Limiting exposure to environmental toxins' above.)

•Patients with self-imposed dietary restrictions – Self-imposed dietary restraints (eg, vegetarian-type diet, gluten-free diet, paleolithic diet) can be problematic if essential nutrients are left out of the diet or weight gain is inadequate. (See 'Issues regarding self-imposed dietary restraints' above and 'Other dietary issues' above.)

•Antigen avoidance/ingestion and allergy in offspring – Neither avoidance nor ingestion of specific antigens, such as peanuts, milk, and eggs, during pregnancy impact the frequency of atopic disease in offspring. (See "Primary prevention of allergic disease: Maternal diet in pregnancy and lactation".)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Edmund F Funai, MD, Jonathan Gillen-Goldstein, MD, Henry Roque, MD, MS, and Jean M Ruvel, RD, CDE, CDN who contributed to an earlier version of this topic review.