Nutrition during Pregnancy and Birth Outcomes

Substantial progress has been made globally in reducing the number of deaths among children <5 years of age – a reduction of 60% compared to levels in 1990 [1]; however, an estimated 4.9 million under-five deaths occurred in the year 2022, 2.3 million of which were during the first month of life [2]. Reducing the number of neonatal deaths remains a key target of the sustainable development goals [3]. Identifying modifiable risk factors, such as nutrition in pregnancy, to optimize newborn health and reduce the risk of neonatal mortality is therefore a major public health priority. This narrative review summarizes the epidemiologic literature and recommendations on nutrition during pregnancy and its associations with birth outcomes.

Newborn vulnerability to mortality in the neonatal period is affected by the timing and size at birth. For over a century, low birth weight, defined as birth weight <2,500 g or 5.51 pounds, has been commonly used as an informative indicator of neonatal mortality [4] driven primarily by robust epidemiological data from the USA (and other Scandinavian countries) that showed stark differences in the neonatal mortality (171.6 per 1,000 live births) among infants born at <2,500 g compared to those born ≥2,500 g (5.5 per 1,000 livebirths) [5]. Infants born between 3,501 and 4,000 g in these seminal studies had the lowest risk of neonatal mortality. However, there are two major processes that contribute to low birth weight – short gestational duration and poor intrauterine growth rate [6]. As such, Lubchenco and colleagues [7] developed the first birth weight-for-gestational age charts to identify infants with the lowest and highest neonatal mortality risks for clinical decision-making and management. Infants born with birth weight below the 10th percentile of the birth weight-for-gestational age curve based on a standard reference population are defined as being small-for-gestational age (SGA), and those above the 90th percentile are classified as being large-for-gestational age (LGA). Today, the INTERGROWTH-21st newborn size-for-gestational age standards, which are based on a geographically and ethnically diverse population of healthy pregnancies, are one of the most widely used and globally accepted newborn size-for-gestational age standards [8], though many high-income countries continue to use nationally developed charts [9].

Children who are born low birth weight, SGA, and preterm (defined as births that occur at <37 completed weeks) – collectively referred to small and vulnerable newborns – have a higher risk of mortality and suboptimal growth and neurodevelopment outcomes later in life [10‒13]. Newborns with macrosomia (defined by birth weight >4,000 g) and LGA are an emerging concern as they are also at a higher risk of neonatal mortality and contribute to higher risk of maternal obstetric complications at delivery, such as cesarean section [14]. Box 1 summarizes the definitions of key adverse birth outcomes. Preventing and reducing the burden of adverse birth outcomes is a key global priority as it affects millions of mothers and newborns yearly, particularly in countries in sub-Saharan Africa and South Asia [15]. Collectively, offspring experiencing adverse outcomes in utero are at higher risk of poor long-term outcomes and chronic diseases [16]. Optimal nutrition during pregnancy therefore has important implications for supporting healthy pregnancies and birth outcomes [17].

Starting with conception, a number of hormonal, metabolic, and physiologic changes occur in healthy pregnancies to support the growth of the placenta, amniotic fluid, mammary glands, blood, adipose tissue, and the fetus [18]. The first half of pregnancy is characterized by increases in hormones to maintain the pregnancy and influence metabolism, while the latter half of pregnancy is characterized by rapid fetal growth [19]. Both basal and postprandial glucose metabolism change over the course of pregnancy to meet the nutritional demands of the mother, the placenta, and the fetus, and are affected by maternal prepregnancy body mass index (BMI) [20]. For example, fasting glucose decreases while insulin secretion increases progressively as pregnancy progresses, with increases in insulin concentration being more pronounced in women with body fat <25% as compared to women with body fat >25% [20]. In insulin-sensitive women, insulin sensitivity most often decreases and is accompanied by an increase in adipose tissue and basal metabolic rate (BMR) [21]. In more insulin-resistant women (e.g., those with obesity), insulin sensitivity often increases and is accompanied by a decrease in BMR and potential increase in lipolysis [22]. Women with normal weight (BMI <18.5 kg/m²) are hypothesized to begin their pregnancies with better insulin sensitivity and therefore experience a greater total decrease in insulin sensitivity in contrast to women with overweight (BMI 25 to <30 kg/m²) or obesity (≥30 kg/m²) with normal glucose tolerance. In addition to changes in glucose metabolism, substantial adaptations occur for lipid metabolism during pregnancy, with the magnitude of increase in maternal adipose tissue in pregnancy being second only to the increases in plasma volume. Between the 10th and 30th week of gestation, approximately 3.3–3.5 kg of fat (up to 4.4 kg has been reported) is deposited for maternal stores before fetal energy demands are at the peak, providing an energy reserve of ∼30,000 kcal, with very little being deposited in the fetus [19, 20, 23]. The majority of fat deposition during pregnancy is subcutaneous and is distributed primarily over the trunk and thighs, which is unique to pregnancy [18]. Women with underweight and normal weight tend to accrue more fat tissue during pregnancy than women with overweight and obesity [20]. Fat accretion parallels total gestational weight gain (correlation coefficient of r = 0.81) and is inversely correlated with prepregnancy weight [18, 24].

The energy intake requirements for a healthy pregnancy can vary substantially due to interindividual variability the in amount of fat deposition, lipid metabolism based on maternal body fat stores at conception, variability in the metabolic rate, and the estimated needs for the deposition of new tissue to support the products of conception [25, 26]. The estimated energy requirement is the average dietary energy intake that is predicted to maintain energy balance in an adult of a defined age, sex, weight, height, and level of physical activity, which during pregnancy also accounts for a women’s prepregnancy BMI and the number of weeks pregnant [25]. Seminal longitudinal pregnancy studies from Scotland, England, the Netherlands, Thailand, The Philippines, and The Gambia were the first to demonstrate stark differences in the total metabolic costs of pregnancy (ranging from +50,200 kcal in Swedish women to −10,750 kcal in unsupplemented Gambian women) and in the pattern of changes in BMR, ranging from a rapid increase in the BMR in response to pregnancy in high-income countries to a delayed increase in BMR in low-income countries, and even a rapid fall in early gestation in the Gambian pregnant women [27, 28]. The cumulative increase in BMR during pregnancy is estimated to range from a relative increase of 5% in the first trimester to 25% in the third trimester compared to the prepregnancy BMR on average [23]. Similarly, there is wide variability in the total energy expenditure during pregnancy due in part to variation in physical activity during pregnancy in well-nourished women and to physiological adaptations to conserve energy in response to low resources [23, 28].

Despite the contextual and interindividual variability in the amount of energy expended for resting metabolic rate, fat gain, and fat-free mass gain [19], the energy requirement for tissue accretion during the first trimester of pregnancy is minimal. As such, the estimated energy requirement during pregnancy is commonly estimated primarily for the second and third trimester of pregnancy [25] when the metabolic costs of the placenta, fetal, and fat tissue synthesis are also greatest [19]. For women in the normal and overweight categories, living in high-income countries, the additional energy needs may be ∼150–250 kcal/day (Table 1), especially if activity levels decline [25, 26, 29]. In underweight women, the energy needs are estimated to be higher at ∼300 kcal/day and may be even higher with high physical demands of daily life common in resource-constrained contexts [19, 25]. Indeed, the joint Food and Agricultural Organization of the United Nations (FAO)/World Health Organization (WHO)/United Nations University (UNU) expert consultation recommended that for women without obesity who seek prenatal care only in the second or third trimester of pregnancy (as is the case in many low- and middle-income countries), may be advised to increase their food intake by 360 kcal/day in the second trimester and by 475 kcal/day in the third trimester [30]. It is important to note however that physiological adaptations in the BMR among energy-constrained pregnant women in The Gambia suggests that energy conservation is prioritized to ensure successful pregnancy in resource-constrained environments [28]. Energy intake above what is needed for the rise in basal metabolism that occurs during pregnancy is therefore likely to be stored as excessive gain in adipose tissue [19]. Indeed, the energy needs for women with obesity are estimated to be negative (−50 kcals/day) during pregnancy [25].

Weight gain during pregnancy is a sensitive measure of maternal nutritional status. In 2009, the Institute of Medicine (IOM) in the USA updated guidelines for the recommended rate of weight gain and the total weight gain during pregnancy to support optimal growth and development of the maternal, placental, and fetal components (shown in Table 1) [18]. Higher magnitude of weight gain is recommended among underweight and normal weight women compared to women with overweight and obesity. These guidelines were developed to balance the risk of adverse maternal outcomes, such as excessive postpartum weight retention and unnecessary cesarean section, as well as adverse newborn outcomes, including neonatal mortality, SGA, and LGA. The American College of Obstetrician and Gynecologists endorses the IOM guidelines for weight gain during pregnancy for all women irrespective of age, parity, smoking history, race, and ethnicity in the USA [31]. These guidelines however may not be directly applicable to all women globally as the data used to develop the IOM recommendations were primary from high-income countries [18]. Ongoing research, led by the World Health Organization (WHO), aims to create global standards for gestational weight gain using data from geographically and ethnically diverse populations [32].

Nonetheless, weight gain outside the IOM guidelines has been consistently associated with adverse maternal and newborn outcomes in high-income and in low- and middle-income countries [33‒36]. In an individual participant data meta-analysis of ∼118,000 pregnancies from 23 low- and middle-income countries, inadequate gestational weight gain (defined as weight gain below 90% of the recommended range by the IOM) was associated with higher risk of having newborns with low birth weight, SGA, short-for-gestational age, and microcephaly, whereas excessive weight gain (defined as weight gain >125% of the recommended range by the IOM) was associated with a higher risk of having newborns with LGA and macrosomia [35]. Women with prepregnancy BMI of underweight, overweight, or obesity had a higher risk of adverse neonatal outcomes associated with suboptimal weight gain (inadequate or excessive) compared with women with normal weight. These findings were consistent with meta-analyses of over 1 million pregnancies primarily from high-income countries [33, 34], though evidence for the association between suboptimal weight gain and preterm birth was inconsistent between studies. Notably, the epidemiology of gestational weight gain adequacy varies substantially between global regions. Women in sub-Saharan Africa and South Asia experience a high burden of inadequate gestational weight gain [37], whereas women in high-income countries are at a higher risk of excessive weight gain during pregnancy, which is also associated with an increased risk of cesarean section delivery and metabolic consequences for the mother in the postpartum period [33].

Recent evidence suggests that the current IOM guidelines may overestimate the lower limit of the amount of weight gain necessary for healthy pregnancy outcomes, particularly for women with overweight and obesity [38]. In a large Swedish longitudinal population-based cohort of 15,760 pregnant individuals with class I, II, and III obesity followed for 8 years, approximately 25% of women, on average, had weight gain below the IOM recommended lower limit of 5 kg, which did not increase the risk of adverse outcomes [39]. Pregnancies in women with class 3 obesity with weight gain below the IOM recommendations or weight loss were associated with a lower risk of adverse outcomes compared with a weight gain of 5 kg. While these data suggest that weight gain below recommendations or weight loss among women with prepregnancy obesity in high-income settings may not be associated with higher risk of adverse birth outcomes, further research is needed to fully elucidate the risks and benefits of weight gain below the IOM recommendations or weight loss for adverse birth outcomes in diverse populations and contexts.

The WHO and the Food and Agriculture Organization of the United Nations (FAO) jointly published an expert consultation report on nutrient goals for preventing chronic diseases [23]. These guidelines provide ranges for population macronutrient intakes for adults in % total energy, with subsequent consultations setting more specific recommendations for absolute intakes in pregnancy [40, 41] (shown in Table 2). The USA and Canada also jointly developed the Dietary Reference Intakes that provide specific guidance for nutrient requirements during pregnancy to meet the physiological increase in demand for nutrients to support maternal, placental, and fetal needs based on the best available evidence (Table 2) [42].

The FAO/WHO recommends that 55–75% of total dietary energy intake should be from carbohydrates, with <10% from free sugars [23]. During pregnancy, carbohydrate needs are based on the requirements for the individual pregnant person plus the requirements for glucose utilization for the fetal brain [44]. The recommended dietary allowance (RDA), which is sufficient to meet the nutrient requirements of nearly all (97–98%) healthy pregnancies, is set at 175 g/day [42]. However, a recent review of maternal macronutrient intakes during pregnancy found wide variability in the average daily carbohydrate intake of women, ranging from 170 g/day in Greece to 345 g/day in China, with the average intakes being above the 175 g/day recommendation across contexts [46]. It has been suggested that current guidelines for carbohydrates may not meet the glucose requirements for placental metabolism, which can be up to 36 g of glucose [47]; as such, a potential increase in the RDA to 220 g/day may be warranted to account for the glucose utilization by the placenta [47].

Globally, fat intake is recommended to be 15–30% of dietary energy consumption, with saturated fatty acid intake recommended to be <10% and long-chain polyunsaturated fatty acids (PUFAs), such as omega-3s and docosahexaenoic acid, recommended to be between 6 and 10% [23]. During pregnancy, the USA/Canada dietary guidelines have defined adequate intake values for linoleic acid and α-linolenic acid – the two essential fatty acids – as at 13 g/day and 1.4 g/day, respectively [42], whereas the FAO/WHO guidelines define minimum requirements as 2% of total energy as part of a healthy diet [40]. These long-chain PUFAs are essential for optimal fetal brain development and have been associated with improved neurodevelopmental outcomes later in life [48, 49] as well as lower risk of preterm birth, though the evidence linking higher long-chain PUFAs intake to birth outcomes has been mixed [50]. As one of the main constituents of membranes and precursors of lipid metabolism, long-chain PUFAs are involved in many regulatory processes including regulation of genes involved in lipid and carbohydrate metabolism and development of neuronal extensions through the establishment and stabilization of synapses and myelination [51]. In a systematic review and meta-analysis of randomized controlled trials comparing omega-3 PUFA interventions, either as supplements or food, during pregnancy with placebo, omega-3 was associated with a lower risk of preterm birth and early preterm birth (<34 weeks of gestational age), perinatal death, and low birth weight, but had little to no effect on SGA and insufficient evidence to evaluate the effect on maternal outcomes [52]. Fatty fish, such as salmon, sardines, and anchovies, are high in omega-3 fatty acids and low in methylmercury; exposure to methylmercury in the prenatal and postnatal period has been associated with deficits in memory, learning, and behavior in children [53, 54].

The RDA for protein for pregnant and lactating women was first established based on extrapolation of nitrogen balance studies conducted in young men. However, more recent evidence using stable isotopes to trace the utilization of a labeled amino acids by the body demonstrates that protein needs increase over the course of pregnancy and are higher than previously thought. The FAO/WHO Expert Committee recommended an additional 1 g/day, 9 g/day, and 31 g/day intake of protein in the first, second, and third trimester of pregnancy, respectively, to support fetal and maternal tissue accretion [41]. In the USA and Canada, the current RDA in pregnancy is 1.1 g protein/kg/day which reflects a change of 1.3 times higher requirement compared to nonpregnant counterparts [44]. There may also be variation in protein requirements over the course of pregnancy, ranging from 1.1 g/kg/day in early pregnancy (11–20 weeks) to 1.52 g/kg/day in late pregnancy (30–38 weeks) [55].

Protein energy intake during pregnancy has been extensively researched, particularly among women with or at risk of undernutrition in pregnancy and/or in low-resource settings [56]. Initially, questions about high-protein intake diets during pregnancy were raised in the 1980s, after a trial reported that a high-protein supplement (where ∼34% of supplement’s energy came from protein) led to higher weight gain and higher risk of neonatal deaths [57], but the results did not reach statistical significance. In underweight women with limited access to food supplies and who are under the demands of physical labor, the consumption of food supplements, even for as short a duration as the last 90 days of pregnancy, may benefit fetal growth – the better the energy supply in such a situation, the better the support for fetal growth and metabolic demands [58].

A recent review of nutritious food supplements in undernourished pregnant women found that women who received balanced energy protein supplements providing macro- and micronutrient content (energy range: 118–1,017 kcals/day, protein range: 3–50 g, fat range: 6–57 g, and other micronutrients) had newborns with improved birth weight and lower risk of stillbirths and SGA, with inferences being similar for women who were provided with lipid nutrient supplements (LNS, energy range: 118–746 kcals, protein range: 3–21 g, fat range: 10–53, and RDA of micronutrients) [59]. There was however substantial heterogeneity in the type and composition of nutritious supplemental foods provided in pregnancy. New trials based on expert consultation on the composition of BEP supplements during pregnancy will provide novel insights on the impact of such supplements on maternal and infant health in the perinatal period [60, 61].

The role of micronutrients during pregnancy has been reviewed in detail previously [62]. Most micronutrient (vitamin and mineral) requirements are increased in pregnancy due to higher maternal, placental, and fetal needs, with marked increases for iron, folate, iodine, choline, and zinc [42, 45, 62] (shown in Table 2). Micronutrients involved in one-carbon metabolism, including folate, vitamin B6, and B12, have an essential role in gametogenesis, fertilization, development, and implantation of the embryo and therefore affect maternal fertility [62, 63]. Folate requirements increase during pregnancy due to rapidly dividing cells related to fetal growth and nucleotide synthesis for fetal and placental development [62], and supplementation with folic acid, a synthetic form of folate, is recommended due to its higher bioavailability. Vitamin A, a fat-soluble vitamin, is crucial for embryonic development as the role of retinoic acid via nuclear receptors is present in all tissues and is involved in gene expression and cell differentiation [64]. The requirements for trace minerals, such as iodine and zinc, also increase during pregnancy. Iodine, essential for the synthesis of thyroid hormone, is involved in the development of brain tissue and is associated with the acquisition of neurodevelopmental skills, including cognition and learning [65, 66]. Zinc is involved in many biological processes, including cell division, protein synthesis and growth, and nucleic acid metabolism [67]. In the latter half of gestation, fetal growth drives the increases in mineral accretion, particularly for calcium, which is required for the mineralization of the fetal skeleton. Vitamin D, a fat-soluble vitamin, which can be synthesized endogenously by the human skin or consumed through animal source foods, further supports bone mineralization and calcium homeostasis [68]. The increase in red blood cell mass and the high placental and fetal needs result in an increase in iron requirements during pregnancy, which is important for hemoglobin synthesis and oxygen transport [62]. Notably, plasma volume expands by an average 48% among pregnant individuals compared to nonpregnant individuals, with the rate of plasma volume increasing steadily in the first trimester, followed by a sharp rise in the second trimester, and a continuous but slow increase in the third trimester [69]. Plasma expands at a higher rate than red blood cells, resulting in hemodilution and a lower hemoglobin cutoff to classify anemia in pregnancy [70]. Micronutrient biomarkers exhibit different patterns depending on the biomarker, increasing, staying the same, or decreasing during pregnancy, and the implications of plasma volume on the circulating micronutrient concentrations are not entirely clear.

Nonetheless, it is well established that the higher needs for micronutrients in pregnancy are challenging to meet through diet alone and are exacerbated when the quality and quantity of diets is low [71, 72]. Indeed, the prevalence of micronutrient deficiencies is high worldwide, affecting a disproportionate number of pregnant women in low- and middle-income countries [71, 73]. Globally, 36% of pregnant women (ranging from 15% in high-income countries to 52% in West and Central African countries) are estimated to be anemic [74], with iron deficiency being the most common cause of anemia [75]. Other common micronutrient deficiencies in women of reproductive age include vitamin D deficiency (63%), zinc deficiency (41%), vitamin A deficiency (ranging from ∼2% in Vietnam to 43% in Pakistan), and iodine deficiency (∼40% in low- and middle-income countries) [71]. While the requirement for dietary calcium is not increased in pregnancy due to increased efficiency in intestinal absorption, dietary calcium intake during pregnancy is on average 647 mg/day in low- and middle-income countries [76], which is well below the 1,000 mg RDA.

Deficiencies in micronutrients have been associated with several adverse birth outcomes. The effect of folic acid deficiency before and during pregnancy on the risk of neural tube defects was among the first micronutrient deficiencies to be identified for its role on birth outcomes that could be corrected with supplementation [77]. Since then, iron deficiency has been identified as a causal risk for anemia during pregnancy resulting in low birth weight; low dietary calcium has been identified to increase the risk of preterm birth and preeclampsia; and iodine deficiency has been associated with an increased risk of adverse neurodevelopmental consequences for the newborn [78].

To address such deficiencies, the WHO has had a longstanding recommendation for all pregnant women to take iron (30–60 mg) and folic acid (400 micro grams) throughout pregnancy [79]. Substantial evidence in the last 2 decades, however, has shown that multiple micronutrient supplements (MMS), which typically contain 15 micronutrients including 30 mg of iron and 400 μg of folic acid, compared to iron-folic acid supplements alone provide a higher magnitude of benefit in preventing low birth weight, preterm birth, and SGA newborns particularly among women who are anemic or underweight [80]. As a result, current WHO guidelines recommend antenatal MMS that include iron (30–60 mg) and folic acid (400 μg) for pregnant women to prevent low birth weight, preterm birth, and SGA in the context of rigorous research [81]. The evidence for the efficacy of MMS is derived mainly from low- and middle-income countries, and, as such, the applicability of prenatal MMS in high-income countries or populations not at risk of multiple nutrient deficiencies, for example, due to adequate diet or large-scale food fortification programs, is unclear [81]. However, a large number of countries, including several countries in Europe, do not have mandatory food fortification programs for vitamins and minerals essential for pregnancy (e.g., folate) [29] and the risk of exceeding the tolerable upper limit for most micronutrients is low [43]. In the USA, prenatal MMS are recommended to meet the nutrient needs during pregnancy and specific attention should be paid to the dose of the 6 micronutrients with the most evidence for potential benefit for maternal and child outcomes: folate, iron, vitamin A, vitamin D, calcium, and omega-3 fatty acids [82]. In addition to benefits associated with MMS, recent evidence suggests that 500 mg per day of calcium supplements has equivalent benefits for preventing preeclampsia and preterm birth compared to the current WHO recommendation of 1,500 mg per day of calcium supplements in contexts with low dietary calcium intake [83]. Research is ongoing to evaluate effective implementation strategies to support scaling-up MMS and to evaluate the acceptability of calcium supplements in various contexts.

The WHO guidelines note that “a healthy diet during pregnancy contains adequate energy, protein, vitamins, and minerals, obtained through the consumption of a variety of foods, including green and orange vegetables, meat, fish, beans, nuts, pasteurized dairy products, and fruits.” [79]. This general guidance is in line with most, if not all, national and international professional societies and governmental organizations. On average, pregnant women’s diets in high-income countries do not align well with recommendations, with dietary intake of total fat and saturated fat being above the recommended amounts and dietary intake of PUFAs, carbohydrates, and fiber being below the recommendations based on country-specific guidelines [84]. Similarly, the dietary intake of folate, iron, and vitamin D are below the recommended amounts in most high-income country regions [83], but calcium intake can vary considerably across countries (e.g., sufficient in Europe but below recommendations in Japan) and the dietary intake of other important micronutrients during pregnancy, such as iodine, are not commonly reported [85].

Pregnant women can achieve the largest variety of nutrients across food groups when they have a balanced diet with moderate protein intake [84, 85]. Higher dietary diversity has been associated with a lower risk of having low birth weight infants, particularly in low- and middle-income countries [86]. Diets and dietary patterns with high levels of vegetables, fruits, whole grains, nuts, legumes and seeds, and seafood intake are associated with a protective effect on preterm birth, whereas dietary patterns with higher intake of red and processed meats and/or fried foods are associated with a higher risk of preterm birth in high-income countries [87]. Importantly, while the consumption of plant-based diets have been shown to be safe and result in normal pregnancy outcomes [88], it is not recommended for omnivorous women to switch to a plant-based diet during pregnancy without accounting for and managing the implications for protein quality as amino acid profiles of the animal and plant-based proteins vary greatly [55]. Recent systematic reviews evaluating the effect of consuming vegetarian and vegan diets during pregnancy found no evidence for adverse maternal-fetal outcomes, provided that potential deficits in vitamin B12 and iron were addressed, though the evidence is based on limited number of observational studies with substantial heterogeneity [89]. Key guidance to support optimal nutrition during pregnancy is summarized in Box 2.

Fetal growth rate in multiple gestations is similar to the growth rate of singleton gestations up to ∼30 weeks gestational age [18]. The IOM guidelines for weight gain during pregnancy are based on observational data from high-income countries and rely on evidence from women with normal weight prepregnancy BMI who gave birth to twins at 37–42 weeks of gestation with an average twin birth weight of ≥2,500 g [18]. The average weight gain in these women ranged from 15.5 to 21.8 kg for twin gestations, 20.5–23.0 kg for triplets, and 20.8–31 kg for quadruplets. While these data are insufficient to qualify as global recommendations for weight gain for multiple gestations, particularly given a lack of data on multiple gestations among underweight women and from diverse population, they provide general guidelines for weight gain during pregnancy for healthy pregnancy outcomes. The macro- and micronutrient needs for women with multiple gestations are also higher and women are recommended to increase their protein intake by an additional 50 g/day beginning in the second trimester of pregnancy [42]. The nutritional needs of pregnant adolescents are also higher than pregnant adults (≥20 years of age) in order to account for the needs of the growing adolescent and the fetal-placental unit. Evidence from individual participant data meta-analysis suggests that gaining inadequate weight gain is associated with a higher risk of neonatal mortality in adolescent pregnancies (<20 years), which remain relatively common in LMICs, compared to pregnancies among women 20–29 years of age [35]. As a result, higher weight gain is recommended among pregnant adolescents (range: 14.6–18 kg) compared to adult pregnant women to support healthy outcomes [18]. In addition, the requirements for some micronutrients for pregnant adolescents, particularly for calcium (RDA of 1,300 mg/day), are higher compared to adult pregnant women [42].

There are many safety concerns in pregnancy, most of which are due to potential harm to the developing fetus. During pregnancy, women are more susceptible to food borne illness due to changes in their immune system [90]. As such, food safety guidelines are stricter during pregnancy. In addition to standard rules about not eating raw or undercooked meats, seafood, or eggs (including dough/batter), pregnant women should be provided with guidance on food preparation (e.g., cooking times and temperature) and on the importance of good hygiene (e.g., hand washing) to avoid the heightened risk of infection with foodborne pathogens [91]. During pregnancy, it is also recommended to (1) not eat cheeses made from unpasteurized milk (often soft cheese) or drink unpasteurized milk, juice, or cider; (2) not eat deli meats and hot dogs (or heat them to steaming hot before eating); (3) not eat refrigerated pates, meat spreads, or smoked seafood (unless cooked or canned); and (4) not eat raw sprouts. These additional rules are due to the heightened risk of contracting Listeria monocytogenes and Toxoplasma gondii during pregnancy. L. monocytogenes can be found in raw meats, seafood, and dairy and T. gondii can be found in many foods including meats and unwashed fruits and vegetables (it is also found in cat feces and pregnant persons should avoid handling cat litter).

Another key risk in pregnancy is the risk of birth defects due to insults in early pregnancy. Vitamin A supplements in high doses (>10,000 IU per day) and retinoid acne medications should be avoided before and during pregnancy as retinol and retinol esters can cause congenital anomalies [92]. Of note, carotenoids such as beta-carotene do not carry a risk of toxicity. Alcohol should also be avoided in pregnancy due to the risk of miscarriage, birth defects, and fetal alcohol spectrum disorder. The World Health Organization, the USA, and many countries have guidelines recommending complete abstinence from alcohol (and illicit drugs) during pregnancy [93, 94].

Optimal nutrition during pregnancy is critical and arguably the most important factor for achieving healthy pregnancy outcomes. A balanced, diverse, and nutritious diet is universally recommended to meet the needs and maintain growth of maternal, placental, and fetal tissues during pregnancy. Daily supplementation with prenatal iron-folic acid or MMS containing iron and folic acid is recommended in most low- and middle-income country settings but is also taken prophylactically by women in high-income countries. Taking prenatal MMS has minimal risks, with important potential benefits for pregnancy outcomes. However, not all supplements are alike, and women should take supplements with the sufficient dose of important nutrients. Women should consume foods during pregnancy that follow a healthy dietary pattern and meet (without exceeding) the higher energy needs for gestational weight gain and optimal pregnancy outcomes.

The authors have no conflicts of interest to declare.

The Nestle Nutrition Institute (NNI) provided an honorarium to N.P. NNI had no role in the conception, design, preparation, or writing of the manuscript.

N.P. wrote the initial draft of the manuscript with critical input from A.G. All authors critically reviewed and revised the manuscript.