May 12 (HealthDay News) -- When taken for at least a year before conception, folic acid supplements can help reduce the chance of a premature birth by at least 50 percent, University of Texas researchers say.

Their study, published in the May 12 issue of PLoS Medicine, found no link to a reduction in the odds of giving birth before 37 weeks of pregnancy if the supplements were taken for less than a year before conception. The researchers also found no ties between adding folic acid, also known as vitamin B9, to a woman's diet and any pregnancy complications.

About 12 percent of U.S. babies are born before 37 weeks' gestation, according to a Public Library of Science news release. Premature babies can having breathing issues, learning or developmental disabilities, and are less likely to survive than those born closer to 40 weeks' gestation. Other research has linked low levels of folate (folic acid) in the mother with a shorter length of pregnancy, the release noted.

The new study, which looked at the pregnancies and childbirth experiences of almost 35,000 women, found that those who took folate supplements for at least one year before conception were 70 percent less likely to spontaneously give birth between 20 and 28 weeks of gestation. These same women were also 50 percent less likely to give birth between weeks 28 and 32.

SOURCE: Public Library of Science, news release, May 11, 2009