Experts trace origin of weight problems to mother’s womb

You may think you know why people 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 per cent 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.

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 nine or more pounds at birth than were women who gained only 18 to 22 pounds.

For each kilogramme (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).

Birth weight

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 August 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.

Risk factors

It found that at age nine, 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.

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.”

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.

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.