The March of Dimes says that women should start taking folic acid for at least a year before they get pregnant.

Doing so cuts their risk of having a premature baby in half -- and possibly as much as 70 percent -- according to a new study.

The study from the University of Texas Medical Branch at Galveston looked at reports from 38,000 women who didn't have major complications.

"We already know that folic acid supplementation beginning before pregnancy and continuing into the first trimester helps prevent serious birth defects of the brain and spinal cord, such as spina bifida," said Dr. Alan R. Fleischman of the March of Dimes. "(This) research ... reinforces our message that every woman of childbearing age should consume 400 micrograms of folic acid daily."

A news release said the drop in very early premature births was particularly notable. Those babies are at the greatest risk for cerebral palsy, retardation, lung disease and blindness.

The reseearch, conducted by Dr. Radek Bukowski was published in the online journal PLoS Medicine.