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 Erica Gunderson of Kaiser Permanente, which runs hospitals and clinics in California.

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 11 pounds (5 kg) 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.

研究人员于本周一称，新妈妈们如果想减掉怀孕期间增加的体重，应该多睡觉，这可要让新妈妈们犯难了。

研究人员发现，在宝宝六个月大时，每天只睡五小时或不足五小时的妈妈在生完孩子一年后不能减掉多余体重的几率是那些睡眠充分的妈妈的三倍。

“凯撒永久”医疗保健机构的埃里卡?甘德森说：“我们知道，对于普通人群来说，睡眠不足会导致体重增加和肥胖，而我们的这项研究表明，女性在产后保持充足的睡眠有助于她们恢复孕前体重，这与健康饮食和锻炼身体同等重要。哪怕每天多睡两个小时，情况就会大不一样。” “凯撒永久”医疗保健机构在加利福尼亚开设有医院和诊所。

甘德森及其同事对940名女性进行了研究，这些女性都参加过波士顿哈佛医学院的产前及产后健康研究。

他们发现，在宝宝六个月大时，每晚只睡五小时或不足五小时的妈妈在生完孩子一年后更难减掉体重，她们在怀孕期间增加的11磅（5公斤）多余体重没有减掉。

而每晚睡眠时间达七小时或七小时以上的妈妈减掉的体重更多。该研究报告在《美国流行病学》期刊上发表。

研究人员承认这可能会让新妈妈们为难，因为婴儿的睡眠是断断续续的。

哈佛医学院及哈佛朝圣保健机构的马修?吉尔曼博士说：“新妈妈们知道这一研究结果后，一定会问，‘那怎样才能既保证孩子的睡眠，又保证我的睡眠？’目前，我们的研究小组正在研究这一重要问题。”