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Weight problems may begin in the womb

NYT: You may think you know why Americans continue to get fatter and develop obesity-related diseases. But the explanation may start long before people have an opportunity to eat too much of the wrong foods and exercise too little.
/ Source: The New York Times

You may think you know why Americans continue to get fatter and develop obesity-related diseases. But the explanation may start long before people have an opportunity to eat too much of the wrong foods and exercise too little.

Increasing evidence indicates that the trouble often starts in the womb, when women gain more weight than is needed to produce a healthy, full-size baby. Excessive weight gain in pregnancy, recent findings show, can result in bigger-than-average babies who are prenatally programmed to become overweight children — who, in turn, are more likely to develop diabetes, heart disease and cancer later in life.

The Institute of Medicine, the health arm of the National Academy of Sciences, reported last year that more than a third of normal-weight women and more than half of overweight and obese women gain more weight than is recommended during pregnancy. Over all, “fewer than 40 percent of pregnant women gain only the recommended amount of weight during their pregnancy,” Dr. Sylvia R. Karasu and Dr. T. Byram Karasu report in their new book “The Gravity of Weight.”

It's not all in the genes
While genes play a role in weight issues for some people, recent studies indicate that genetics is not the main reason babies are born too fat. Rather, the new evidence suggests that in addition to gaining significantly more weight than is recommended during pregnancy, more women now start out fatter before they become pregnant.

The latest study controlled for the effects of genetics by studying consecutive pregnancies among more than half a million women. The analysis, by Janet Currie, a health economist at Columbia University, and Dr. David S. Ludwig of Children’s Hospital Boston, found a consistent association between the amount of weight a woman gained during pregnancy and the birth weight of her babies.

Women who gained more than 53 pounds during a full-term pregnancy with one baby were more than twice as likely to have babies who weighed 9 or more pounds at birth than were women who gained only 18 to 22 pounds. For each kilogram (2.2 pounds) of weight gained by the pregnant mother, the baby’s birth weight increased by 7.35 grams (one-fourth of an ounce).

Because birth weight tends to predict body mass index later in life, “these findings suggest that excessive weight gain during pregnancy could raise the long-term risk of obesity-related disease in offspring,” the authors concluded in their report, published online in The Lancet on Aug. 5.

The analysis sought to rule out the effects of genetics on birth weight by comparing each married woman’s pregnancy weight gain and birth weight of her babies in successive pregnancies that occurred within a few years of each other (and thus were most likely to involve the same father). Although the authors did not know how much the women weighed before becoming pregnant each time, other studies have found that many women fail to lose all their pregnancy weight before they become pregnant again. Thus, they are likely to start out fatter and gain more during the next pregnancy.

In an accompanying editorial, Dr. Neal Halfon and Dr. Michael C. Lu of the Center for Healthier Children, Families and Communities at the University of California, Los Angeles, cited still another study, this one based on data gathered from parents and children in Britain. It found that at age 9, the children of women who had gained more weight than recommended by the Institute of Medicine were fatter than other children, more likely to become overweight, and had several risk factors for heart disease — including higher blood pressure and lower levels of protective HDL cholesterol — as well as poorer immune function.

This study, published in Circulation in June, found that a woman’s weight before pregnancy was even more important than excessive weight gain during pregnancy in predicting a number of risks for the baby: birth complications, excessive baby fat and “metabolic abnormalities associated with poor health outcomes, including childhood obesity,” as the editorial put it.

Latest recommendations
Dr. Halfon, a pediatrician, said in an interview, “The little changes in children’s metabolism tend to be compounded over time and become big changes in adults.”

The latest recommendations from the Institute of Medicine, revised last year, suggest these pregnancy weight gains, as determined by a woman’s prepregnancy weight:

  • 28 to 40 pounds for thin women, with a B.M.I. of 18.5 or lower.
  • 25 to 35 pounds for normal-weight women, with a body mass index of 18.6 to 24.9.
  • 15 to 25 pounds for overweight women, with a body mass index of 25 to 29.9.
  • 11 to 20 pounds for obese women, with a body mass index of 30 or higher.

Dr. Lu, an obstetrician, said prepregnancy weights in nine states revealed significant increases in overweight and obesity between the periods 1993-94 and 2002-3. Even normal-weight women are now more likely to gain excessive amounts during pregnancy than were women who became pregnant in the 1990s, according to data from the national Centers for Disease Control and Prevention.

According to data from the National Center for Health Statistics, since 1990 proportionately more women have gained more than 40 pounds in a singleton pregnancy.

Higher birth weights
The new findings suggest that Americans are now caught in a vicious cycle of increasing fatness, with prospective mothers starting out fatter, gaining more weight during pregnancy and giving birth to babies who are destined to become overweight adults.

“There are a lot more high-birth-weight babies being born,” Dr. Currie said in an interview, “and this may have something to do with the increase in overweight we’re now seeing in the population over all.”

When I was pregnant 40-odd years ago, a normal-weight woman was expected to keep her pregnancy weight gain to within 24 pounds. But, Dr. Currie said, about 20 years ago the concern about too many babies with low birth weights may have prompted many doctors to be less restrictive about how much weight women gained while pregnant.

“We still see a lot of low-birth-weight babies, but the number of high-birth-weight babies has increased quite dramatically,” Dr. Currie said. “There’s no reason for a woman to gain more than 40 pounds with a single baby. We used to think babies in the womb were well protected, but we now know they are influenced by lots of things that will affect them later in life.”

She added, “The next frontier has to be the prepregnancy period. If we really want to improve the health of children, we have to get to mothers before they get pregnant.”

As Dr. Halfon said, “You can’t turn around in the nine months of pregnancy what’s been going on for many years of life. The preconception period is critical to placing pregnancy on a healthier trajectory.”

This is the second of two columns about weight. Last week’s was . This article, "Weight Problems May Begin in the Womb," first appeared in The New York Times.