BEIJING, April 3 (Xinhuanet) -- It's too soon to tell if standard pregnancy weight gain advice should be abandoned, but a recent study suggests fat mothers run four times the risk of giving birth to a child who will be overweight at age 3, compared to women who gain less than the advised amount.

    The problem is defining how much weight is overweight. According to the study, even accepted weight gains may raise the risk of having an overweight child, and the result was about the same for women who gained more than the advisable amount.

    Lisa Bodner, an assistant professor of epidemiology and obstetrics-gynecology at the University of Pittsburgh Graduate School of Public Health, says the new work adds to previous indications Institute of Medicine guidelines issued in 1990 may need to be revised. IOM is a private non-governmental organization that advises the federal government.

    Bodner, who didn't participate in the new study, called it one of the most rigorous to address the question.

    "We know that weight gain is important, we just have to find a middle ground" between too little and too much, she said.

    Dr. Emily Oken of Harvard Medical School and the study's lead author said it's clear a pregnant woman shouldn't gain more weight than recommended.

    But beyond that, it's too early to say whether women should try to gain less than the standards call for or shoot for the low end of the recommended range, Oken said. At least the latter course is probably safe, she said.

    Some other experts urged that pregnant women not try to gain less weight than recommended.

    In any case, Oken said, it's too soon to call for a revision of the standard guidelines.

    Oken said it's not clear why greater weight gain in the mother would raise the risk that her toddler would be overweight. She noted women who have diabetes during pregnancy tend to produce bigger babies who run a heightened risk of becoming overweight later in life. That suggests some factor in the womb can affect a baby's future, she said.

    Oken said gaining too much weight also carries risk for the mother, such as not being able to lose that weight and so being overweight or obese herself. Gaining too much weight raises the risk for having a baby that is too large, which may lead to a difficult delivery or Caesarean section, she said.

    But gaining too little weight in pregnancy raises the risk of having a low-birthweight baby, which poses a hazard to the child.

    So figuring out the proper weight gain is a balancing act, she said.

    The study appears in the April issue of the American Journal of Obstetrics & Gynecology.

    (Agencies)