Normal-weight women who gain more than the 24 to 35 pounds during pregnancy recommended by the Institute of Medicine are 74 percent more likely to be unsuccessful at breast-feeding than mothers who observe these guidelines, according to a new study conducted by Cornell University/Bassett Hospital researchers.

However, women who are obese before pregnancy do not further increase their already high risk of lactation failure, regardless of their weight gain after conception.

"Our findings suggest that obese women already have reached before conception a critical level of fatness for lactation failure," says Kathleen Rasmussen, professor of nutritional sciences at Cornell University and the lead researcher on the study. She will present her findings April 2 at Experimental Biology 2001, a meeting of the Federation of American Societies for Experimental Biology in Orlando, Florida.

The researchers defined unsuccessful breast-feeding as no longer breastfeeding on the fourth day after giving birth.

Whether and how long mothers breast-feed is important because breast milk can protect children from a variety of childhood illnesses, says Rasmussen. The United States public health goals, spelled out in Healthy People 2010, call for 75 percent of America's new mothers to start breastfeeding, 50 percent to continue for six months and 25 percent for 12 months

"We're a long way from those goals nationally. At the present time, 64 percent of women breast-feed right after pregnancy but only 29 percent continue for at least six months," Rasmussen says.

In 1997, Rasmussen reported that overweight and obese mothers – whether or not they had gained the extra pounds during pregnancy – were 2.5 to 3.6 times, respectively, less successful in starting breast-feeding than their normal-weight counterparts, and the heavier the mother, the less successful she was at breast-feeding. The current study of 2,494 women who had single births at Bassett Hospital in Cooperstown, N.Y., over a nine-year period sought to identify whether weight gain during pregnancy played a significant role. Rasmussen reports that 60 percent of the women in the study were normal weight at conception but that 46 percent of these women gained more weight during their pregnancy than recommended. Among the women who were overweight and obese at conception, 72 percent and 70 percent, respectively, exceeded weight guidelines during pregnancy.

"That excess weight gain significantly changed the likelihood these women could initiate breast-feeding successfully even though all the women in the study wanted to and attempted to breast-feed," says Rasmussen, an expert in pregnancy and lactation. "Thus far, we have established weight-gain guidelines for pregnant women with the baby's health in mind but these findings suggest we should also think about a mother's ability to breast-feed."

The study was part of the doctoral thesis by Julie Hilson, Cornell Ph.D 2000, and was conducted with Chris L. Kjolhede of Bassett Hospital.

The current study confirms the research team's previous finding that obese women also are at significantly higher risk for discontinuing breast-feeding much sooner than normal-weight mothers. Rasmussen said she suspects the reasons why obese women have trouble breast-feeding are a combination of biological, mechanical and psychosocial factors.

Rasmussen stresses the importance of being normal weight at conception and keeping weight gain during pregnancy within recommended levels to maximize success at breastfeeding.

The study was supported, in part, by a training grant from the National Institutes of Health and the U.S. Department of Agriculture via a Hatch grant.