Old health advice often dies hard. This is particularly true - perhaps dangerously so - of historic advice for pregnant women, according to a new Viewpoint published Tuesday in the Journal of the American Medical Association.

Most adults remember the traditional guidelines for expectant mothers. Get as much rest as possible during your pregnancy, even prolonged bed rest if complications arise. At the same time, "eat for two" - you and your developing child. According to the new report, however, "these misguided recommendations" have "evolved into a major contributor to the worldwide obesity epidemic."

Fifty years ago, gynecological medicine emphasised the need for women to gain enough weight to provide for healthy fetal growth. Now the coin has been flipped.

About 45 per cent of current mothers-to-be begin their pregnancy in an overweight or obese state, vs. 24 per cent in 1983. In addition, nearly half of pregnant women now gain more weight in nine months than the amounts recommended by the Institute of Medicine. Those guidelines are ordered by body mass index of the woman - normal, overweight or obese - and stand at 25 to 35 pounds, 15 to 25 pounds, and 11 to 20 pounds.