WASHINGTON - RESEARCHERS presented a conundrum to new mothers on Monday, saying that women who want to lose the extra weight gained in pregnancy should try to get more sleep.

They found that mothers who slept five hours or less a day when their babies were six months old were three times more likely than more rested mothers to have kept on the extra weight at one year.

'We've known for some time that sleep deprivation is associated with weight gain and obesity in the general population, but this study shows that getting enough sleep - even just two hours more - may be as important as a healthy diet and exercise for new mothers to return to their pre-pregnancy weight,' said Ms Erica Gunderson of Kaiser Permanente, which runs hospitals and clinics in California.

Ms Gunderson and colleagues studied 940 women taking part in a study of prenatal and postnatal health at Harvard Medical School in Boston.

The women who slept five hours or less a night when their babies were six months old were more likely to have kept on 5kg of weight one year after giving birth, they found.

Women who slept seven hours a night or more lost more weight, they reported in the American Journal of Epidemiology.

The researchers acknowledged this may pose a dilemma to new mothers, given that infants sleep so fitfully.

'With the results of this study, new mothers must be wondering, 'How can I get more sleep for both me and my baby?' Our team is working on new studies to answer this important question,' said Dr Matthew Gillman of Harvard Medical School and Harvard Pilgrim Health Care. -- REUTERS