Moms who eat healthy before they become pregnant lower the risk of their babies having heart abnormalities when they're born, says a new study published in the Archives of Disease in Childhood.

Congenital heart defects affect about 1 percent of American newborns, and about one in four of those children will die in infancy. Although some heart conditions are caused by abnormal genes or chromosomes, the reason for many heart defects remains a mystery, and doctors had little advice to offer their patients in the way of preventive measures.

Some studies indicate a vitamin supplement might help, while others suggest a healthy diet might lower the risk.

To explore the role of diet, researchers questioned approximately 19,000 women about their diet in the year leading up to the time they became pregnant. The women were a part of the National Birth Defects Prevention Study.

Half of the women had babies with major heart abnormalities, and half gave birth to healthy babies between 1997 and 2009.

Moms who ranked in the top 25 percent of diet quality had a significantly lower risk of giving birth to a baby with certain heart defects — as much as 37 percent — than women who were in the bottom 25 percent.

Earlier studies had found links between diet and other birth defects, including cleft palate and neural tube defects.

The new study reinforces current advice for women wanting to get pregnant.