About 1 in every 33 babies born in the United States has a birth defect, according to the CDC. A birth defect, also called a congenital anomaly, is a difference in how a baby’s body forms or works that is present at birth. Most happen in the first months of pregnancy.

What causes birth defects

For most birth defects, the cause isn’t known. Researchers believe many come from a mix of genes, health conditions, medicines, and the environment. Because the cause usually isn’t known, many birth defects can’t be prevented. Some can, and folic acid is the best-proven example.

The birth defects folic acid helps prevent

Folic acid lowers the risk of neural tube defects (NTDs), serious birth defects of the brain and spine. Taking 400 micrograms (mcg) a day before and during early pregnancy is recommended by the CDC and the U.S. Preventive Services Task Force.

  • Spina bifida happens when the backbone that protects the spinal cord doesn’t form and close as it should. It can damage the spinal cord and nerves and cause problems with walking and with bladder and bowel control. See our article on what causes spina bifida.
  • Anencephaly happens when much of the brain and skull don’t develop. Almost all babies with anencephaly die before or shortly after birth.

Since the U.S. began adding folic acid to enriched grains in 1998, NTD rates have dropped by 28%, and about 1,300 babies a year are born without an NTD who otherwise would have had one, according to the CDC.

Other birth defects: what we know

You may see folic acid credited with preventing heart defects, cleft lip and palate, limb differences, and kidney or bladder defects. Some studies suggest a benefit, but a review of the clinical trials found the evidence too limited to say for sure, according to the NIH. Folic acid’s proven benefit is for neural tube defects.

Other steps that lower the risk of birth defects

  • Don’t drink alcohol while pregnant or trying to get pregnant. There’s no known safe amount, according to the CDC.
  • Don’t smoke, and avoid secondhand smoke. Smoking in pregnancy is linked to cleft lip and palate, preterm birth, and SIDS, according to the CDC.
  • Talk with your doctor or midwife about every medicine and supplement you take, before pregnancy if you can.
  • If you have diabetes, work with your provider to get your blood sugar in range before pregnancy.
  • Avoid infections you can prevent. For example, have someone else change the cat litter, and avoid raw or undercooked meat. Our tips for a healthy pregnancy have more.

Updated October 2026. This page is for general information and is not a substitute for advice from your health care provider.

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