High trans fat consumption by mothers during the second trimester of pregnancy is linked to larger babies, according to a study conducted at the Harvard School of Public Health exploring the impact of trans fats on fetal growth.

"We’ve been worried about the effects of trans fats for years," said HSPH Associate Professor Eric B. Rimm, co-writer of the study.

The results suggest that trans fats are not only harmful for adults—among whom high trans fat consumption can lead to increased risk of coronary heart disease—but also for their babies.

The babies appear to have a higher risk for adult diabetes and obesity later in life, according to Juliana F. W. Cohen, lead writer and a student at the HSPH. In addition, mothers of larger children may require Caesarean sections.

"It’s amazing that something we consume in such small amounts could have such large implications," said Rimm, who emphasized that women who are pregnant should remain conscious of their trans fat consumption, especially at restaurants.

With each incremental increase in trans fat consumption during the second trimester, babies grew marginally. To compare fetal growth and adjust for the length of gestation, the researchers used "Z-scores," the measurement of a baby’s birth weight corresponding to the baby’s week of birth.

Trans fats appear to block the transfer to the fetus of DHA, an omega-3 fatty acid often found in fish, according to Cohen. Previous Harvard research has linked DHA to decreased fetal growth.

Researchers surveyed almost 1,400 women who completed questionnaires about their diets during the first and second trimesters of pregnancy. There was no correlation between trans fat consumption and fetal growth during the first trimester.

Trans fats often occur in processed foods, such as french fries, baked goods, and commercial junk foods. Natural foods, such as milk and meat, also contain trans fats in slightly lower quantities. The study—to be published in the upcoming November issue of The American Journal of Clinical Nutrition—indicated that both sources of trans fats led to larger children.

Although researchers focused primarily on the effects of trans fats, the questionnaires tracked consumption of a wide range of foods.

Researchers adjusted for potentially distorting factors—including race, socioeconomic status, and income—by including these variables in their model.

But more research into the topic is still necessary said Cohen, noting that other variables could have created inconsistencies in the data.

"I definitely recommend that future studies look into this association," Cohen said.