Medical researchers have known for some time that it is important for pregnant women to have folic acid in their diets in order to have a healthy baby. And for a long time, doctors have told pregnant women to take folic acid supplements in order to prevent certain kinds of birth defects. Now they're finding that women need to have the right amount of folic acid even before they get pregnant if they want healthy babies.  

However, gynecologist Radic Bukowski from the University of Texas Medical Branch explains doctors don't know exactly how much of the vitamin is the correct amount, nor do they know how long a woman should take it.

Bukowski looked at data from about 38,000 pregnant women around the United States. They had answered questionnaires about what they ate before and during their pregnancies.

"We collected very carefully different information and data, including information if women took folic acid before becoming pregnant and for how long they have done this before becoming pregnant," he says.

Folic acid helps the body make DNA and other genetic material. It's found in green leafy vegetables and in some kinds of meats as well. In addition, in the United States, folic acid is also found in many grains.  Most commercially produced grains have been fortified with the vitamin since the 1990s. This helps guarantee that women get plenty of the vitamin while they're pregnant.

But Bukowski found that women who took folic acid supplements for a year or longer before becoming pregnant had a significantly lower risk of having a preterm birth than the women who did not take a folic acid supplement regularly.

"The reduction was really huge," Bukowski says. "It was 70 percent lower risk of delivering between 20 and 28 weeks - this is the very premature babies, the ones who have most of the problems. And they're the ones who ? likely not survive."

Bukowski also found that there was a 50 percent reduction of preterm birth between 28 and 32 weeks, also a very high risk group.

There was no change in the risk for delivering after 32 weeks.

Bukowski says this is another piece of data in a growing body of evidence showing that the health of a woman before she gets pregnant is important for her baby's health.  

"It seems to me that many of the complications of pregnancy - having a small baby, for example, or delivering prematurely - the origins of these problems seems to be at least in part at the beginning of pregnancy or maybe even before," Bukowski says.   

"There are some also animal studies that support that? that health before pregnancy or in the very early stages of pregnancy are very important for what is going to happen in the end."

Bukowski says he'd like to find out how folic acid interacts with other nutrients and exactly how it works to help babies get a healthy start in life.

His research is published in the journal PLoS Medicine.