Folic acid, already recommended for women of childbearing age because it lowers the risk of spina bifida and related birth defects, also might cut the chances of delivering a premature baby by half or more, scientists report today.
The new analysis is based on folic acid supplements, as opposed to folic acid in food, reported by 34,480 pregnant women in a U.S. government-sponsored trial.
Taking supplemental folic acid -- either by itself or in a multivitamin -- for at least a year before conceiving was tied to a 70% lower risk of delivering between 20 and 28 weeks' gestation and a 50% lower risk of delivering between 28 and 32 weeks. A full-term delivery occurs after at least 37 weeks.
Accounting for preterm birth risk factors such as previous preterm birth, obesity and older age did not substantially change the findings, according to an abstract for the study. It is being presented in Dallas at the annual meeting of the Society for Maternal-Fetal Medicine.
"Obviously, these findings are very exciting and very promising, not the least because of the simplicity of the findings and the ease of potential implementation," says lead author Radek Bukowski, an assistant professor of obstetrics and gynecology at the University of Texas Medical Branch at Galveston.
Because about half of all pregnancies are unplanned, the March of Dimes and other groups recommend that all women who could conceive take 400 micrograms of synthetic folic acid daily. The supplement reduces the risk of neural tube birth defects by up to 70%, says Janis Biermann, March of Dimes senior vice president for education and health promotion.
The neural tube, precursor to the brain and spinal cord, normally closes by day 28 of gestation, often before women even know they're pregnant.
A survey in late 2007 of U.S. women ages 18 to 45 found that only 40% reported taking folic acid daily, Biermann says.
The new study "is promising," University of Pittsburgh epidemiologist Janet Catov says.
In the August issue of the American Journal of Epidemiology, Catov and her co-authors published a study of 1,823 women early in pregnancy that found those who reported taking a multivitamin regularly in the previous six months were 70% less likely to deliver a baby before 34 weeks. Catov says more research is needed to determine what deserves the credit: the folic acid, something else in multivitamins or some characteristic of women who opt to take them.
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