Women who take multivitamins before becoming pregnant are less likely to give birth to premature babies, new study findings suggest.

According to the research, conducted at the University of North Carolina at Chapel Hill, women who took multivitamins before conceiving were half as likely to deliver their babies before 37 weeks of pregnancy.

However, continuing the multivitamins through the first months of pregnancy appeared to have no influence on the risk of prematurity, according to the American Journal of Epidemiology report.

Study author Dr. Anjel Vahratian explained that multivitamins contain folic acid, a B vitamin that, when taken early in pregnancy, helps prevent birth defects in the brain and spinal cord. Previous research suggests that folic acid may improve the placental environment, which helps fetal growth during the last months of pregnancy.

Since half of U.S. pregnancies are unplanned, it’s important for women who may become pregnant to always take folic acid, just in case, the researcher noted.

And although the study suggests that vitamins during pregnancy had no effect on prematurity, that does not mean they offer no benefits, Vahratian said.

“Public health professionals should continue to encourage women to take a daily multivitamin prior to conception and in pregnancy, as part of a healthy diet,” the researcher said.

Most of the previous research on how maternal nutrition influences fetal outcomes has focused on how women ate during pregnancy, rather than before.

To investigate how women’s diet before conceiving affects a fetus, Vahratian’s team asked 2,010 women between their 24th and 29th weeks of pregnancy about their use of multivitamins before and during their pregnancies, then followed them and noted who gave birth prematurely.

Approximately 30 percent of women said they took multivitamins before and during their pregnancies, and another 54 percent said they started taking the pills only once they knew they were pregnant.

Vitamin-users were, on average, older, married, more educated and financially secure.

Ninety-three women said they only took multivitamins before conceiving. These women also reported the highest rates of nausea or vomiting, which may explain why they did not continue the vitamins after they became pregnant.

Only five of these women gave birth prematurely, a lower rate of prematurity than that seen in nonusers, in women who took vitamins before and during pregnancy, and in those who started vitamins once they became pregnant.

Vahratian, now based at the University of Michigan in Ann Arbor, noted that the benefits associated with multivitamins may not stem from the vitamins themselves.

“The protective effect noted in preconceptional multivitamin users may be a proxy for overall healthiness - that women who take a multivitamin prior to pregnancy may be a healthier subset of the general population,” Vahratian told Reuters Health.

SOURCE: American Journal of Epidemiology, November 1 2004.