WEDNESDAY, Nov. 28 (HealthDay News) -- If your new baby is keeping you awake at night, take note: A first-of-its-kind study suggests that sleep deprivation after giving birth may limit a new mother's ability to shed those pregnancy-related pounds.

It's not clear why there may be a link between sleep loss and lack of weight loss. Still, the possibility of a connection is intriguing, said study lead author Erica P. Gunderson, an investigator with the Kaiser Permanente Division of Research in Oakland, Calif.

"Getting enough sleep may be as important as a healthy diet and physical activity to returning to pre-pregnancy weight," Gunderson said.

According to the study authors, scientists have linked low amounts of sleep to obesity, heart disease and diabetes. But there's been little research into the connection between sleep and pregnancy and weight.

For the new study, the researchers looked at the weights and sleep patterns of 940 women who enrolled in a study in Massachusetts during early pregnancy from 1999 to 2002.

A year after giving birth, 124 of the women retained at least 11 pounds of the weight they had gained during pregnancy. After the researchers adjusted the statistics to take into account such factors as family income, they found that women who slept five hours a day six months after giving birth were more than three times likelier to keep weight on compared to women who slept seven hours.

Sleeping six, seven or eight hours a day didn't appear to raise a woman's risk of keeping on weight. "Basically, the women who were sleeping fewer hours did not lose as much weight as women who slept several more hours," Gunderson said.

The study findings, by researchers at Kaiser Permanente and Harvard Medical School/Harvard Pilgrim Health Care, were published in the November issue of the American Journal of Epidemiology.

It might seem that people who sleep less would actually lose more weight, because they'd spend more time burning calories while awake. But the study suggests the opposite, Gunderson said, perhaps because people become hungrier due to lack of sleep.

Also, she added, "If you're awake more, you may have more opportunities to eat."

Claire D. Brindis, a professor of pediatrics at the University of California, San Francisco, said her own experience of giving birth to two children taught her about how stress, sleep and weight are all connected.

"Having lived this, it's partly that you're more tired, and you feel you need food to keep you energized," she said. "And when you're stressed, you feel like you can reward yourself with food. It creates a sense of comfort."

Gunderson said the next step is to understand what women who sleep less after pregnancy have in common. Doctors can then "target women who may not be getting enough sleep and find ways to support them," she said.

More information

To learn more about sleep, visit the National Sleep Foundation.

SOURCES: Erica P. Gunderson, Ph.D., investigator, Kaiser Permanente Division of Research, Oakland, Calif.; Claire D. Brindis, Dr.P.H., professor of pediatrics, University of California, San Francisco; November 2007, American Journal of Epidemiology

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