Pregnant women who consume trans fats from snack foods, fast food and other less-than-ideal fare may give birth to bigger babies, according to a US study.

The study, reported in the American Journal of Clinical Nutrition, centered on nearly 1,400 pregnant women. It found that the higher the woman's intake of trans fats - which raise "bad" LDL cholesterol, but also lower heart-healthy HDL cholesterol - during the second trimester of pregnancy, the larger her newborn was.

The study did not prove that trans fats alone boost fetal growth, and if they did, it is unclear how harmful that could be. But there are risks to having a larger-than-normal newborn, says lead researcher Juliana Cohen, of the Harvard School of Public Health in Boston.

Big babies may have to be delivered by Cesarean-section and studies have found that they may have increased risks of diabetes and heart disease later in life, Cohen adds.

"It's prudent to limit trans fats in your diet anyway. Pregnant women may want to think about how (the fats) could affect fetal growth as well," she says.