Seventy-three percent of obese women studied in a Swedish obesity clinic identified weight gain in pregnancy as an important element in their long-term weight control. On average, the women reported retaining more than 22 pounds after each pregnancy. Such large weight gains after pregnancy are not typical and research shows that most women retain about one pound two to three years after childbirth. But because more dramatic gains can have serious long-term ramifications, it's worth paying attention to how much weight you gain while pregnant and retain afterward.

From the 1950s to the early 1970s, doctors advised women to limit weight gain in pregnancy to 10 to 20 pounds in order to keep a baby's weight low enough to facilitate an easier delivery and to avoid the need for new mothers to lose weight later. Then research began to uncover links between low birth weight babies and mental retardation, learning disabilities and other health complications. As a result, the recommended weight gain range was increased to 20 to 25 pounds in 1970 and then to 25 to 35 pounds in the 1980s. But this higher range was not ideal for everyone.

Another revision led to the current recommendations issued by the Institute of Medicine (IOM) in 1990. These guidelines base ideal gain on the weight status of the mother prior to pregnancy. Women whose body mass index (BMI) classifies them as underweight are advised to gain 28 to 40 pounds to decrease the risk of low birth weight babies. Women starting pregnancy at a healthy BMI are advised to gain 25 to 35 pounds. Women overweight or obese before pregnancy are advised to gain 15 to 25 pounds. Staying within these guidelines may help reduce the mother's risk of gestational diabetes, high blood pressure and the need for a Cesarean delivery.

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The Stockholm Pregnant and Women's Nutrition (SPAWN) study is a follow-up study that has followed about 500 Swedish women through pregnancy and for more than a decade post-partum. Fifteen years after delivery, most participants were slightly heavier compared to their pre-pregnancy weight. However, those whose pregnancy gains were greater than is currently recommended had gained more weight and were more likely to be overweight or obese than those who gained within the limits.

These findings echo a recent study out of Cornell University. At one year after childbirth, the average woman retained just over three pounds beyond her early pregnancy weight. Larger gains during pregnancy, however, increased the odds that a woman would retain an extra ten pounds or more.

In the SPAWN study, weight at one year post-partum was the best predictor of overweight at 15 years. Study authors suggest that it may take a year for women to lose weight gained in pregnancy. The take-home message: Women who have not lost excess pregnancy weight at one year should make lifestyle changes to reduce risk of long-term weight retention.

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Not all women who gain beyond recommendations have trouble returning to their pre-pregnancy weight. Water retention and other medical problems during pregnancy may lead to excess gain without reflecting permanent results. It's not clear whether weight gain in pregnancy could have some biological impact that makes the weight gained harder to lose, or if weight retention reflects eating and exercise habits adopted during pregnancy that are not changed after delivery.

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The IOM may begin evaluating whether further changes in guidelines are needed, but for now, following the current recommended limits is the best advice. As a general rule, women should continue normal calorie consumption during the first three months of pregnancy, add an extra 340 calories daily in months 4 to 6, and increase by about 450 calories for the final three months of pregnancy.