Kathy Perusse has four children — two before weight-loss surgery and two afterward. Her two oldest have trouble maintaining their weight much like she did before the operation. Scientists say there might be a connection.

NEW YORK — When Kathy Perusse had weight-loss surgery and shed 120 pounds, she might have done more than make her own life easier.

She went on to have two daughters, and she might have boosted their chances of avoiding becoming obese, like her two older children are.

That's the implication of research suggesting something in an obese woman's womb can program her fetus toward becoming a fat child and adult. It's not about simply passing along genes that promote obesity; it's some sort of still-mysterious signal.

The idea has only recently entered conversations between doctors and female patients, and scientists are scrambling to track down a biological explanation. That knowledge, in turn, might provide new ways to block obesity from crossing generations.

While there's some disagreement on how important the womb signal is, "the evidence is building and building that it is a substantial issue," said Dr. Matthew Gillman of Harvard Medical School, who studies prevention of obesity.

Others agree.

"I think it could be a hugely significant factor," said Robert Waterland of the Baylor College of Medicine in Houston, who studies the effect in mice.

Dr. Rudy Leibel, an obesity expert at Columbia University, said he doubts it plays a huge role, but still believes it's worth studying. If scientists can uncover its biological underpinnings, he said, they might be able to use that knowledge to prevent or treat obesity from other causes.

Perusse, 39, of Three Rivers, Quebec, knows the effects of being very fat. Before her weight-loss surgery in 1995, she packed 284 pounds on her 5-foot-2 frame. She could not ride a bike or climb stairs to her second-floor home without stopping to rest. Now, although she's still overweight, those limitations are history, she said.

But her older children struggle with their weight. At 5-foot-3 and 300 pounds, her 22-year-old daughter can't bathe her own two children, Perusse said. Her 16-year-old son weighs 230 pounds and stands 5-foot-6. They were born before she had the weight-loss surgery. Her two younger daughters, ages 4 and 7, came along afterward. Their weights are normal so far, though Perusse said her older children weren't overweight at those ages either.

So she's using diet and exercise to try to protect them against what she called rotten genes, including those from their 400-pound father. She said she isn't optimistic.

But Dr. John Kral of the SUNY Downstate Medical Center in New York said his research suggests obese women who lose weight before pregnancy might be helping the next generation keep off excess pounds — even if fat-promoting genes run in the family.

With researchers at Laval Hospital in Quebec, Kral has studied children of severely obese women who were born before or after their mother's weight-loss surgery. They found that, in comparison to children born before surgery, those born afterward were far less likely to be severely obese.

In addition, those born afterward showed lower levels of blood fats and indicators of future diabetes.

Kral said families typically don't change lifestyle or diet after surgery, so that doesn't explain the outcome.

Instead, he said, the surgical bypass operation made the women's bodies less efficient at digesting and absorbing food, and lowered levels of sugar and fat in the blood. That, in turn, would reduce the number of calories delivered to the fetus to levels like those provided by a normal-weight mother, he said.

And the women's shedding of pounds before the pregnancy would also help, he said.