The researchers from Kaiser Permanente and Harvard Medical School believe their study is the first to examine the impact of sleep deprivation on weight retention in mothers after their baby is born.

While other studies have looked at the effect of sleep deprivation on mothers' cognitive and emotional health, associated weight gain has not been considered.

Dr. Erica P. Gunderson, a researcher with Kaiser Permanente and the lead author of the study, says it is well known that sleep deprivation is associated with weight gain and obesity in the general population.

Dr. Gunderson says the study shows that getting enough sleep, even two hours more, may be as important as a healthy diet and exercise for new mothers to return to their pre-pregnancy weight.

The study also found that mothers who slept fewer hours one year after the birth of their baby had twice the risk of substantial weight retention.

Other research has demonstrated that persistent sleep deprivation causes hormonal changes that may stimulate appetite; too little sleep has not only been linked to obesity in women, but also coronary artery disease and diabetes.

Of course welcome as any new research is which enhances our understanding of the human body, new mothers struggling to cope with fractious infants are bound to ponder what they are realistically able to do about a lack of sleep, particularly if they have other young children.

The new study used data from Harvard's Project Viva, which is looking at the prenatal and postnatal health of a group of 940 women with an average age of 33 years.

The women were questioned about their sleep habits and weight at the six-month and one-year postpartum assessments; forty-seven percent of the women were first-time mothers, 37 percent had two children, and 16 percent had three or more children.

Kaiser Permanente says a new baby's first year at home is a hard adjustment for everyone and the organisation provides support for mothers in the form of pregnancy e-newsletters, newborn clubs, online health encyclopedia, online programs, podcasts, videos, weight and exercise programs, and discounts for gym memberships and Weight Watchers enrollment.

But the researchers say the best advice of all for mothers struggling to cope with new babies is to ask for help and to get some support.

The study was funded by the National Institutes of Health, Harvard Medical School and Harvard Pilgrim Health Care Foundation.