In general, it is known that pregnancy is associated with increased nutritional needs due to physiological changes and the metabolic/nutritional demands of the embryo and fetus.
Pregnancy causes numerous and immediate changes within the body, including an increase in plasma (component of the blood) and urination which can affect how nutrients are used. Researchers are still learning what these changes mean for nutrition requirements for pregnant women, which is debated often.
Researchers are attempting to determine:
How are water-soluble and fat-soluble nutrients treated within the pregnant body?
Do specific nutrient requirements increase, decrease, or stay the same?
How does each specific nutrient affect fetal development?
Can a specific nutrient possibly prevent pregnancy-related complications, even if women are not deficient? (i.e. folic acid)
If supplementation is necessary, what dose and in what form (i.e. food or pill) is most optimal?
A big hurdle regarding recommendations is that the medical community does not know with certainty at which point a pregnant woman is considered “deficient” in most nutrients, which complicates recommendations and causes conflicting study conclusions.
Learning various aspects of how nutrients are used, stored, excreted, and transferred to the fetus during pregnancy is critical, as it is likely that both too little or too much of certain nutrients can be harmful during pregnancy.
Further, researchers have known for awhile that the nutritional status of pregnant women can potentially affect the infant into adulthood and influence their metabolic health as early as childhood (known as the Barker hypothesis or “fetal programming").
For additional background:
Essential nutrients: nutrients the body cannot make enough of on its own must be obtained from the diet (see below section)
Water soluble: vitamins that dissolve in water, or require water for absorption; most excess water-soluble vitamins are excreted in the urine; includes vitamin B1 (thiamin), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B5 (pantothenic acid), vitamin B6 (pyridoxine), vitamin B7 (biotin), vitamin B9 (folic acid), and vitamin B12 (cobalamin) and vitamin C (ascorbic acid)
There are 13 essential vitamins: A, C, D, E, K and the B series, including B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folic acid) and B12 (cobalamin), sufficient levels of each are vital during pregnancy.
The Food and Nutrition Board (FNB) of the National Academy of Medicine (formerly the Institute of Medicine) establishes specific dietary reference intakes for each nutrient in the United States.
Although there are specific recommendations for pregnant women, these are only recommendations – determining the true amount of each nutrient pregnant women need across the board is exceptionally difficult.
Note: Most recommendations are offered in a specific amount of either micrograms or milligrams per day for mostly point of reference; women do not need to specifically keep track with a notebook or journal of the nutrient value of their food unless specifically instructed to do so by their HCP.
For background, values are usually indicated as:
Recommended dietary allowance: the average daily dietary intake level of a nutrient sufficient to meet the requirements; for most micronutrients, the RDA or AI for pregnant women is slightly increased compared to non-pregnant women of the same age
Adequate intake: when evidence is not available to establish an RDA, an adequate intake is estimated, which is determined to be an amount necessary to avoid deficiency
Tolerable upper intake level: the highest level of daily intake that is likely to pose no risk of adverse health effects in almost all individuals per a specific age
The thresholds for nutrient intakes to support good pregnancy outcomes are not fixed values but based on averages. Nutrient needs vary widely from woman to woman depending on her pre-pregnancy nutritional status and health, fetal size, diet, lifestyle, metabolism, and genetics.
Overall: Fertility and Fetal Growth
Current research continues to illustrate how the overall nutritional health of pregnant women in the periconceptional period – when women are actively trying to conceive – may have marked improvements for early embryonic development and may be more important than later in pregnancy.
After fertilization, the fertilized egg and early blastocyst appear to detect and respond to the nutritional quality of the Fallopian tube environment, even before implantation. Further, during the 4th week, the embryoblast receives "nutrients" from endometrial blood vessels, glands, and cells.
Maternal nutrition during early development is associated with positive embryo/fetal growth, organ development, and body composition and function. Further, adjustments in nutrient metabolism are apparent within the first weeks of pregnancy.
Early nutrition status can also affect placental development which in turn, is responsible for transporting nutrients and oxygen to the fetus.
Additionally, a study published in July 2021 used an animal model to determine that maternal malnutrition can adversely affect early heart development. This could potentially lead to heart problems when the offspring becomes an adult. The study indicated that nutrient restriction led to an inability to deliver sufficient energy to cardiac tissues. However, a separate study published in August 2022 indicated there was not enough evidence to confidently conclude if maternal micronutrient deficiencies increase the risk of fetal congenital heart disease. Further large-scale prospective studies are necessary.
It is also assessed that maternal metabolism during early pregnancy is mostly anabolic, where a pregnant woman’s body essentially hoards nutrients in preparation for the second half of pregnancy.
If maternal nutrition status/energy reserves are low at conception, the basal metabolic rate is downregulated to conserve energy. This can cause the mother/baby to gain weight faster as pregnancy progresses, leading to possible health complication for both, to include insulin resistance and less fetal growth of muscle and bone.
In the second half of pregnancy, nutrition plays a major role in fetal growth:
More than 90% of fetal growth (fat, muscle, bone) occurs in the second half of gestation, and a woman’s diet during this time is one of the most important factors associated with adequate growth. During the third trimester, the mother’s metabolism is mostly catabolic – rapidly transporting nutrients to the fetus.
Further, a pregnant woman’s poor diet and nutritional status in late pregnancy could alter the stress response of the fetus, which could affect that infant into adulthood.
What was understood in prior generations regarding maternal nutrition has changed due to advances in molecular and cellular techniques, as well as the introduction of new foods, cooking methods, and trendy diets.
"New" concerns or questions regarding nutrition during pregnancy is not a result of paranoia, but of a much better understanding of how certain nutrients and foods (e.g. listeria, choline, iodine) affect a pregnancy, and this includes the mother's health. Women should partake in well-balanced diets with varied food sources of each nutrient, while consuming favorite foods in moderation.
For example: Clinical trial results published in June 2021 found that adherence to alternate Healthy Eating Index (AHEI), alternate Mediterranean diet (AMED), and Dietary Approaches to Stop Hypertension (DASH) during periconception and pregnancy were related to lower risks of gestational diabetes, gestational hypertension, preeclampsia, and preterm delivery. Note: Women should talk to their health care provider before changing their diet during pregnancy.
Prenatal vitamins are helpful for those who may require them based on deficiencies in their diet, but these vitamins should not, and do not, replace a healthy diet. Women do not need to be concerned if they miss a daily dose.
With the exception of folic acid, there is currently no strong evidence that supplementation of any nutrient, beyond what can be obtained through the diet, has any additional benefit during pregnancy (but choline and iodine may require considerations).
Sole deficiency of one nutrient or moderate deficiency of many does not appear to increase the risk for miscarriage – even in extreme cases; however, fetal growth could be affected.
Carbohydrates are a necessary aspect of fetal growth and should not be restricted (quality over quantity) unless specifically directed by an HCP.
Specifically high protein diets (e.g. keto diet) are not recommended during pregnancy.
Iodine deficiency in pregnant women is becoming an increasing concern in the last 10 to 20 years mostly due to trendy consumption of salts that do not contain iodine.
Sodium/salt restriction may not be necessary in otherwise healthy pregnant women.
Hydration is very important due to the body’s requirement for additional fluid during pregnancy, but no specific amount of water per woman has been determined (individualized).
There is currently no strong evidence that a gluten-free diet during pregnancy has any benefit for women who do not have a gastrointestinal disorder.
Women concerned about their nutrition in early pregnancy due to nausea/vomiting should talk to their HCP; however, research indicates that the early embryo/fetus can tolerate this condition well, unless it is severe, or leads to dehydration or significant weight loss.
Proper weight gain during pregnancy has been debated for decades. Current guidelines indicate that staying within recommended weight guidelines based on pre-pregnancy weight may lead to the most optimal outcomes, but gaining/losing on either side does not mean complications will occur. Overall nutrition may be far more important.
Prenatal vitamins are vitamins that claim to be specially formulated to meet recommended nutrient values for pregnant women. It has been determined that multi-nutrient supplements can significantly reduce the frequency of birth defects and maternal complications, but are still often debated in their necessity and formulations.
Vitamin consumption prior to and during pregnancy has increased due to very public and well-advertised recommendations by health professionals.
Women need to take prenatal vitamins as recommended by their HCP. However, based on current research regarding what is known about nutritional needs during pregnancy, women should not be concerned if they miss a day or two of their vitamins.
Most additional nutrient requirements during pregnancy can be met through a varied diet of animal and plant sources. Prenatal vitamins can help women round out their nutrition, while also supplying an adequate intake of folic acid. Prenatal vitamins do not replace a healthy diet.
Women who cannot tolerate multivitamins well, especially those containing iron, have many different options, to include vitamins with only a few nutrients. These women should call and have a discussion with their HCP.
It is recommended all pregnant women eat a balanced diet rich in fruits and vegetables, high-quality carbohydrates, and a variable mix of proteins from beans, lean meats, fish, and seafood (for amino acids).
Diets should also be limited with added sugar, red meat, and processed foods. This guidance is offered mostly due to a lack of knowledge regarding exact nutritional needs during pregnancy.
However, women are also encouraged to consume a diet of moderation – to include cravings and “unhealthy” items. Women may find it harder to stick to a healthier diet overall if they completely eliminate their favorite foods.
In uncomplicated pregnancies with no dietary conditions, the well-rounded diet described above is expected to supply all vitamins and minerals necessary for a health pregnancy, with an exceptions for folic acid (and/or iron in some cases).
Women have individualized nutritional needs, and recommendations should consider a woman’s access to food, overall health, underlying metabolic conditions, socioeconomic status, race/ethnicity, cultural food choices, and body mass index. Women should also understand that adjustments to their diet may be made based on conditions that may arise during pregnancy (i.e. gestational diabetes).
Regarding safe food options, although the list of foods that may be harmful during pregnancy appears to be growing as science/technology improves, most foods are safe when women/partners practice proper hygienic food preparation.
Additionally, some foods do require certain considerations. Read more on food safety here, and read the pages listed below for additional, specific information.
Partners can help women during their pregnancy by aiming to eat healthier themselves, in an effort to support the woman in her own eating and exercise habits. Couples who strive to eat healthier, make smarter choices, and engage in more physical activity together, are more likely to be successful.