CHICAGO — To the long list of problems scientists now link to obesity, add one more: infertility.

Doctors helping couples trying to get pregnant long have noticed the connection between added girth and difficulty conceiving.

"That association is pretty well established," said Dr. Roger Lobo, a reproductive endocrinologist at Columbia University. Heavy women often don't ovulate normally because their hormones are out of whack. If they lose just 5 percent of their body weight, he said, "some will ovulate and even get pregnant with no further intervention."

Gynecologists and fertility experts routinely tell their obese patients to lose weight. But that's easier said than done. So some fertility clinics now are looking for new and better ways to help.

Dr. Laurence Jacobs of Fertility Centers of Illinois thinks he has found one in the form of a program he calls "Fit & Fertile," in which patients wear an adjustable-weight vest to boost the effect of whatever exercise they do. Since March, when the pilot program got under way with 17 infertile women, 8 have gotten pregnant, "a much better rate than we would have anticipated in this group of women," Jacobs said.

One of those is Naomi Scianna, 39, who is expecting her second child in April. Scianna needed fertility drugs to get pregnant with 19-month-old Joey. When she and her husband decided to try again, she said, "I was two years older, and I had never lost the weight I gained with Joey, so it was much harder."

Scianna, like most of Jacobs' patients, suffers from a condition known as polycystic ovarian syndrome, in which a hormone imbalance interferes with normal egg production. She agreed to join "Fit & Fertile," which involved attending support sessions and exercising with an X2 vest, donated by the manufacturer.

"I lost 10 or 11 pounds," Scianna said, "which may not sound like a whole lot. But my body was resistant to insulin, and getting in better shape helped manage my insulin. That played a major role in our success."

Andrea Evans, 34, is still trying. Both she and her husband try to walk at least 30 minutes a day while wearing their vests, which she admits doesn't always happen. Evans, who has lost 16 pounds since March, has added weights to her vest gradually and is now up to 8 pounds.

Jacobs said he lost 20 pounds using an X2 and continues to walk with it 40 minutes a day, five or six days a week.

"It's not a silver bullet," he said. "You still need to have some degree of motivation. But the vest reminds you that you have to put it on and do something with it."