Before she even thinks about getting pregnant, a woman’s health status can have a critical impact on the health of her future baby, experts say.

Taking folic acid — the synthetic form of the vitamin folate — at least three to six months before conception makes a woman 70 percent less likely to have a baby with a birth defect, said Jeannette Sebes McDonald, infant mortality reduction coordinator with the local health department.

“I think there’s a huge misconception that, once you’re pregnant, you get on your prenatal vitamins and all is well, but you’ve missed the opportunity to get that 70 percent reduction if you haven’t been taking it,” she said.

About half of all pregnancies are unplanned, making regular consumption of the vitamin — even for those not intending to have a baby — more critical, according to local health department officials, who this week are recognizing National Folic Acid Awareness Week.

Folic acid, a B vitamin, can help prevent spinal and brain birth defects, such as spina bifida and anencephaly, said Jill Alliman, nurse midwife at the Women’s Wellness and Maternity Center, a birth and women’s health center in Monroe County, Tenn.

“The brain and spinal chord develop so early on in the pregnancy, many women don’t even know they’re pregnant yet when these important developments are happening,” she said.

Health officials recommend that women take a folic acid supplement daily to ensure they are getting the recommended 400 micrograms a day.

Many foods naturally contain folate, and all enriched cereals and grain products in the United State are fortified with folic acid. However, only one-third of U.S. women get the recommended amount, Ms. McDonald said.

Women also can take too much folic acid, according to the U.S. Department of Health and Human Services. More than 1,000 micrograms of folic acid a day may cause nerve damage in people who do not have enough vitamin B12, such as those who are 50 or older and vegans. Vitamin B12 can be found in meat, dairy products and eggs.