Prenatal Vitamins: What Pregnant Women Need to Know

Health Letter, December 2015

By Sarah Sorscher, J.D., M.P.H.

Women seeking to become pregnant are now routinely advised by doctors to start taking a prenatal vitamin before conception and continue throughout pregnancy.[1] These vitamins can be expensive, costing up to $20 for a small box, far more than a standard adult multivitamin.

These expensive prenatal vitamins come with a long list of ingredients that appear to be specially formulated for pregnant women, including folic acid, iron, omega-3 fatty acids, vitamin D and calcium. But do women really need all of these ingredients to have a healthy pregnancy? It turns out that there is little evidence showing that the vast majority of ingredients in prenatal vitamins offer clinically important benefits for otherwise healthy women.

Only one ingredient, folic acid, has proven beneficial as a standard prenatal supplement offered to all women, and this ingredient is commonly available in standard multivitamins, not just those labeled “prenatal.” Learning to look for the right amounts of this key ingredient can help pregnant women save substantially in the vitamins aisle.

Folic acid: An essential vitamin in pregnancy

While many vitamins and minerals are important during pregnancy, women can usually obtain enough of these nutrients by eating a healthy, varied diet. The one major exception to this is folic acid, sometimes called folate. Folic acid is a B vitamin that is naturally found in many foods, particularly dark green leafy vegetables such as spinach. In the U.S., rice, pasta, bread and other grain products are enriched with folic acid, thanks to a government program that began in 1998.[2]

Folic acid is important during pregnancy because deficiency in folic acid can cause serious birth defects known as neural tube defects.[3] These defects can develop in the first month of pregnancy, before a woman even knows she is pregnant.[4] To avoid this deficiency, the Institute of Medicine (IOM), which sets the recommended daily values that often are used on nutrition labels, recommends that all women who could potentially have children get at least 400 micrograms of folic acid per day.[5]

A woman’s need for folic acid increases during pregnancy.[6] To keep up with this demand, the IOM recommends that pregnant women consume at least 600 micrograms per day through dietary sources and supplements.[7]

Birth defects related to folic acid deficiency have declined dramatically in the U.S. since the folic acid enrichment program began, as more women now receive enough folic acid simply by eating regular foods.[8] For example, a bowl of Cheerios now contains 200 micrograms of folic acid per serving, or half of a daily supply for a non-pregnant woman.[9]

Yet in spite of the large number of dietary sources of folic acid, many pregnant women cannot obtain adequate levels through diet alone. For this reason, all women who are pregnant or considering having children should also take folic acid as a dietary supplement.[10]

Many prenatal vitamins contain 800 micrograms of folic acid or more, well over the daily amount recommended for pregnancy. There is little evidence that this high level of folic acid is beneficial for women who eat a healthy diet and have no history of deficiency.

Studies have shown that giving women 400 micrograms per day as a dietary supplement is enough to dramatically reduce the risk of birth defects.[11] Most pregnant women would be better off sticking to a dietary supplement that contains 400 micrograms per day of folic acid or less, and getting the rest of the necessary daily amount of folic acid from dietary sources.

Other ingredients in prenatal supplements

Many other ingredients often are recommended as important components of a prenatal multivitamin. The best-studied of these include iron, the omega-3 fatty acid docosahexaenoic acid (DHA), calcium and vitamin D.[12] Yet other than folic acid, none of these nutrients has been clearly shown to positively affect health when given as a routine dietary supplement to pregnant women who have no evidence of a nutrient deficiency.

Iron deficiency is common during pregnancy,[13] but iron is commonly available in fortified cereals, spinach, red meat and beans. Studies so far have failed to show consistently that providing iron supplements routinely to pregnant women leads to meaningful health benefits for mothers or children.[14],[15] Also, consuming too much oral iron can lead to temporary but unpleasant gastrointestinal problems, including constipation, nausea and abdominal pain.

DHA, another popular ingredient often advertised in prenatal vitamins, is a particular type of omega-3 fatty acid that can be derived from fish oil. The ingredient has many supposed benefits, from decreasing pre-term births to enhancing babies’ performance on mental tests.[16] Yet benefits observed in women who consume high levels of DHA could just as easily be due to the lifestyles and overall good health of the women, rather than the DHA itself. So far, the many randomized studies designed to test DHA’s benefit as a dietary supplement have failed to provide strong evidence of important health improvements for otherwise well-nourished women and their babies, either during pregnancy or in early childhood.[17],[18],[19],[20],[21],[22],[23],[24]

Calcium and vitamin D are important nutrients for pregnant women, particularly during the third trimester, when the bones of the developing baby are growing rapidly.[25] Yet healthy pregnant women who have access to a varied diet generally do not need supplements to get enough of either nutrient.[26],[27] Pregnant adult women should aim to get at least 1,000 milligrams per day of calcium, about equal to the calcium in three and a half eight-ounce glasses of milk.[28] In addition, eggs, fish, and fortified milks and cheeses can provide high amounts of vitamin D, a vitamin that also is naturally synthesized by the body during exposure to sunlight.

What women should do

The best nutrition comes from eating a healthy diet rich in a variety of vegetables, fruits, whole grains, lean proteins and low-fat dairy products. If you follow a healthy diet and have not been diagnosed with a vitamin deficiency, most of the nutrients in prenatal supplements will not be necessary.

To avoid folic acid deficiency, women who are pregnant or considering pregnancy should look for a dietary supplement that contains 400 micrograms of folic acid per day. The least expensive option for this will often be a generic multivitamin or a stand-alone pill that contains folic acid alone. Higher doses of folic acid and other nutrients found in expensive prenatal vitamins are generally not necessary for women who have not been diagnosed with a vitamin deficiency by their doctor.


References

[1] Mayo Clinic. Pregnancy week by week. May 13, 2015. http://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-vitamins/art-20046945’pg=2. Accessed October 26, 2015.

[2] National Institutes of Health, Office of Dietary Supplements. Folate: Dietary Supplement Fact Sheet. December 14, 2012. https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/. Accessed October 26, 2015.

[3] Ibid.

[4] Ibid.

[5] Institute of Medicine. Dietary Reference Intakes: Vitamins. http://www.nationalacademies.org/hmd/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Vitamins.pdf. Accessed October 26, 2015.

[6] National Institutes of Health, Office of Dietary Supplements. Folate: Dietary Supplement Fact Sheet. December 14, 2012. https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/. Accessed October 26, 2015.

[7] Institute of Medicine. Dietary Reference Intakes: Vitamins. http://www.nationalacademies.org/hmd/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Vitamins.pdf. Accessed October 26, 2015.

[8] National Institutes of Health, Office of Dietary Supplements. Folate“ Dietary Supplement Fact Sheet. December 14, 2012. https://ods.od.nih.gov/factsheets/Folate-HealthProfessional/. Accessed October 26, 2015.

[9] Cheerios product website. The One and Only (nutrition information). http://www.cheerios.com/Products/Cheerios. Accessed November 20, 2015.

[10] Wolfe T, Witkop CT, Miller T, Syed S. Folic acid supplementation for the prevention of neural tube defects: An update of the evidence for the U.S. Preventive Services Task Force. Evidence Synthesis Number 70. Agency for Healthcare Research and Quality; May 2009. AHRG Publication No. 09-05132-EF-1.

[11] Ibid.

[12] Mayo Clinic. Pregnancy week by week. May 13, 2015. http://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-vitamins/art-20046945’pg=1. Accessed October 26, 2015.

[13] National Institutes of Health. Iron: Dietary Supplement Fact Sheet. October 6, 2015. https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/. Accessed October 26, 2015.

[14] Peña-Rosas JP, De-Regil LM, Dowswell T, Viteri FE. Daily oral iron supplementation during pregnancy. Cochrane Database Syst Rev. 2012;12:CD004736.

[15] Siu A. Screening for iron deficiency anemia and iron supplementation in pregnant women to improve maternal health and birth outcomes: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med. 2015;163:529-536.

[16] Jordan RG1. Prenatal omega-3 fatty acids: Review and recommendations. J Midwifery Womens Health. 2010;55(6):520-8.

[17] Ramakrishnan U, Stinger A, DiGirolamo AM, et al. Prenatal docosahexaenoic acid supplementation and offspring development at 18 months: Randomized controlled trial. PLoS One. 2015;10(8):e0120065.

[18] Gonzalez-Casanova I, Stein AD, Hao W, et al. Prenatal supplementation with docosahexaenoic acid has no effect on growth through 60 months of age. J Nutr. 2015;145(6):1330-1334. http://www.ncbi.nlm.nih.gov/pubmed/25926416.

[19] Zhou SJ, Yelland L, McPhee AJ, et al. Fish-oil supplementation in pregnancy does not reduce the risk of gestational diabetes or preeclampsia. Am J Clin Nutr. 2012;95(6):1378-1384.

[20] Smithers LG, Gibson RA, Makrides M. Maternal supplementation with docosahexaenoic acid during pregnancy does not affect early visual development in the infant: A randomized controlled trial. Am J Clin Nutr. 2011;93(6):1293-1299.

[21] Makrides M, Gould JF, Gawlik NR, et al. Four-Year Follow-up of Children Born to Women in a Randomized Trial of Prenatal DHA Supplementation. JAMA. 2014;311(17):1802-1804.

[22] Larqué E, Gil-Sánchez A, Prieto-Sánchez MT, Koletzko B. Omega 3 fatty acids, gestation and pregnancy outcomes. Br J Nutr. 2012;107 Suppl 2:S77-84.

[23] Makrides M, Gibson RA, McPhee AJ, et al. Effect of DHA supplementation during pregnancy on maternal depression and neurodevelopment of young children: a randomized controlled trial. JAMA. 2010;304(15):1675-83.

[24] Ramakrishnan U, Stein AD, Parra-Cabrera S, et al. Effects of docosahexaenoic acid supplementation during pregnancy on gestational age and size at birth: randomized, double-blind, placebo-controlled trial in Mexico. Food Nutr Bull. 2010;31(2 Suppl):S108-16.

[25] Mayo Clinic. Pregnancy week by week. May 13, 2015. http://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-vitamins/art-20046945’pg=2. Accessed October 26, 2015.

[26] World Health Organization. Guideline: Vitamin D Supplementation in Pregnant Women. 2012.

[27] World Health Organization. Guideline: Calcium Supplementation in Pregnant Women. 2013.

[28] National Institutes of Health, Office of Dietary Supplements. Calcium: Dietary Supplement Fact Sheet. https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/. Accessed October 27, 2015.