Expecting? Better put down that Big Gulp.

A new study by Harvard University researchers has found that pregnant women who forgo sugar-sweetened beverages — specifically soda and fruit drinks — may help their children avoid excess weight and even obesity later in childhood.

"We found mothers who consumed more sugary beverages in mid-pregnancy had children with higher amounts of body fat, no matter what the kids' intake was," said Sheryl L. Rifas-Shiman, a biostatistician with Harvard Medical School and Harvard Pilgrim Health Care Institute.

The research, being published Monday in the journal Pediatrics, is part of Project Viva, a multi-part ongoing study to examine numerous factors' effects on child development before and after birth. The project receives funding from the National Institutes of Health.

"Childhood obesity is widespread and hard to treat," Rifas-Shiman said. "So it's important to identify modifiable factors that occur prenatally and during infancy so that prevention can start early."

Sugar-sweetened beverages have become major targets in efforts to prevent obesity in children and adults. In numerous studies, sugary-drink intake has been linked to excess weight, metabolic syndrome, and type 2 diabetes.

The study's findings involved nearly 1,100 Massachusetts mother-child pairs. Researchers looked at the women's sugary and nonsugary beverage intake during the first and second trimesters of pregnancy between 1999 and 2002. The mothers filled out several questionnaires, and the researchers conducted in-home visits, including one when the children were in middle childhood, with a median age of nearly 8.

Among 8-year-old boys and girls of average height, their weights were about a half-pound more for each additional serving per day of sugary beverages their mother consumed in her second trimester, Rifas-Shiman said.

For 8-year-olds who drank at least half a sugary drink a week and whose mothers consumed at least two sugary beverages a day during mid-pregnancy, the children's weights were about two pounds more. The results were nearly the same among the children who drank less than that if their mothers drank the sugary beverages in pregnancy.

The researchers used a computer program to equalize certain maternal and child variables, such as maternal education, household income, and child gender.

The worst weight outcomes appeared to be linked to mothers who consumed soda, followed by sugary fruit drinks.

"We found that replacing sugary beverages with water. 100 percent fruit juice, or milk had a greater beneficial effect on child weight than did replacing the sugar-sweetened beverages with diet soda," Rifas-Shiman said. Diet soda consumption was associated with slightly higher fat levels.

The study suggests that children's weight gain may have a more developmental cause and that other characteristics of the drinks, including the sweeteners used, may matter more than high calories alone.

The second trimester is a time when fetal fat accumulation is accelerating, Rifas-Shiman said. It may also be a time, she said, that is a sensitive period for development changes "that could have lifelong consequences for obesity."

The researchers believe the study shows evidence of a link between mothers' sugary drink consumption and their children's weight and body fat. Next, Rifas-Shiman said, they are looking at how and when children's consumption of sugary beverages, as well as other factors like diet, has the most impact.