American kids are getting fatter and fatter, and blame for the epidemic of obesity has been laid on soft drinks, video games, lack of gym class, and other potential culprits.

But many of those children were fat as toddlers, which couldn't have been caused by excess Nintendo time. Researchers increasingly think that "programming" in the womb may affect a young child's weight, and researchers at Ohio State University say they've uncovered a key clue. Women who are overweight just before they get pregnant are far more likely to have a child who becomes fat. An overweight woman's child is nearly three times as likely to be overweight by age 7, according to the study, which was published in this month's Pediatrics.

About 21 percent of the children of overweight or obese mothers are also fat. Among black and Hispanic 7-year-olds, the overweight rate was 4 to 6 percentage points higher.

The heavier the mom, the more likely that the child would be overweight early on. And toddlers who were fat were more likely to stay fat.

The study, which analyzed data on 3,022 children in a national health survey of mothers and their offspring, also found that women who smoked while pregnant were more likely to have children who became fat early on. The implications for children are dire, because it's becoming increasingly clear that being overweight early in life makes it more likely that a person will stay fat and thus will be far more likely to suffer diabetes, heart disease, and other deadly diseases.

It's still unclear how much of a role genetics and home environment play in the tendency of the child to become fat. But Pam Salsberry, a researcher at the Ohio State University College of Nursing who led the study, says the message to doctors and prospective mothers is clear:

• Women of childbearing age must get their weight under control before becoming pregnant.
• Pediatricians should intervene as early as possible.

"If there's a family with a history, you should recognize that child is at risk and use preventive strategies before you have a child with an overweight problem at age 5 or 6."