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They’re often called “prenatal vitamins,” but these supplements supply much more. In addition to serving as a back-up for any nutritional gaps in your diet, a prenatal supplement approved by your doctor can help reduce risk for some birth defects, preterm birth and low birth weight baby, while helping you to maintain your own health during pregnancy.

What Prenatal Vitamins Provide

Nutrition experts say a healthy diet is the ideal way to get the nutrients you and your baby require.

"Trouble is, many women in their childbearing years don’t get the nutrients they need, including folic acid and iron. In addition, the requirements for several vitamins and minerals increase during pregnancy," says Hillary Wright. MEd, RD, author of The PCOS Diet Plan: A Natural Approach to Health for Women with Polycystic Ovary Syndrome and director of nutrition counseling at the Domar Center for Mind Body Health at Boston IVF in Waltham, Mass. 

Folic Acid Before Conception

Folic acid is a necessary part of fetal development in the days immediately after conception, so it's best to make sure you're getting the daily requirement before you get pregnant. Because it's difficult to confirm a pregnancy immediately after conception, women should be getting enough folic acid in their diet before getting pregnant. Folic acid is necessary to cover important fetal development requirements during the first weeks of early pregnancy -- when a woman might not yet know that she's pregnant. Experts recommend 400 micrograms (mcg) a day for women capable of becoming pregnant. 

"The most important work of folic acid is done early in pregnancy, sometimes before a woman realizes she’s having a baby," says Shieva Ghofrany, MD, an obstetrician and gynecologist in Stamford, Conn.

During the first 30 days of pregnancy, folic acid helps to prevent defects of the neural tube, which becomes the spinal cord and brain. Pregnant women also need folic acid throughout pregnancy to support rapid cell production. Prescription prenatal vitamins often contain 1,000 mcg of folic acid. Over-the-counter prenatal pills may have upwards of 800 mcg.