Prenatal supplements, also known as prenatal vitamins, are supplements commonly taken by women during the pre-conception period and throughout pregnancy to ensure that both the mother and the fetus receive the appropriate amount of essential nutrients. Despite being referred to as “prenatal vitamins”, they typically include a combination of 3 or more vitamins and minerals. These may encompass vitamins vitamin B1, vitamin B2, B3, vitamin B6, vitamin B12, C, D, E, and K, along with folic acid, iodine, magnesium, iron, copper, zinc, selenium, and sometimes additional components like omega-3.^[3][4]

It is generally recommended for all pregnant women to take at least iron and folic acid to support proper fetal development, and to prevent anemia and other complications during pregnancy. However, especially in low- and middle-income countries, women may experience multiple micronutrient deficiencies, and thus a prenatal multi-micronutrient supplement might be more suitable.^[5]

During pregnancy, when nutritional requirements are higher, micronutrient deficiencies can have adverse health and development consequences (e.g., preterm birth, small for gestational age, low birth weight). In many countries, it is recommended that women take prenatal supplements during pregnancy, typically containing a combination of iron and folic acid plus other vitamins and minerals.^[4]

One meta-analysis, which included women of different gestational ages in low-income and middle-income countries, revealed that supplementation with a multiple-micronutrient (MMN) supplement (i.e., one containing 3 or more micronutrients) reduced the risk of low birth weight infants and the risk of babies considered small for gestational age more than supplementation with just iron and folic acid (IFA); this effect was especially pronounced with supplements containing more than 4 micronutrients. MMN supplementation also lowered the risk of stillbirth and the occurrence of diarrhea in children. Moreover, MNN slightly increased maternal and child serum retinol levels, slightly increased maternal zinc and vitamin B12 levels, and improved executive function scores in children, compared to IFA. However, no difference was noted for all other studied outcomes, including maternal or perinatal mortality, risk of miscarriage, risk of congenital anomalies, preterm births, risk of C-section, child general intelligence, motor functioning, verbal comprehension, or language.^[4] While studies such as this one suggest benefits from taking an MMN prenatal supplement instead of one that only contains folic acid and iron, variations in methods and interventions used, such as supplement composition, may need to be addressed before drawing generalized conclusions.

Whether MMN supplements are more beneficial than just IFA in upper-middle-income and high-income countries remains unclear: it likely varies depending on the intake of essential micronutrients from the diet.^[6]

Prenatal supplements are generally considered safe and well-tolerated when taken at the recommended dosage. However, it’s important not to exceed the recommended daily intake during pregnancy, as higher doses of certain vitamins and minerals may be harmful to the fetus (e.g., iron, folic acid, zinc). Studies specifically addressing the risks of exceeding the upper limit (UL) of these micronutrients during pregnancy are lacking, except for vitamin A. Excessive intake of vitamin A (above 3000 μg)^[7] during pregnancy is known to have teratogenic (i.e., birth-defect-causing) effects.^[1][2] In some prenatal supplements, vitamin A is substituted with beta-carotene, which is converted into vitamin A naturally by the body as required and does not appear to be teratogenic at high doses.^[8]

Another potential side effect of taking prenatal vitamins and minerals is constipation, primarily caused by iron.^[9]

Prenatal supplements contain a blend of different vitamins, minerals, and other nutrients, all of which are known to play a crucial role in various biological reactions and metabolic activities, thereby promoting maternal health and supporting fetal growth. Therefore, there is more than one mechanism of action involved, depending on the micronutrient composition of each supplement. For detailed information on how each micronutrient functions in the body, please refer to the individual pages dedicated to those specific nutrients.