Women who get pregnant after weight-loss surgery tend to be healthier and less likely to deliver a baby born with complications compared to obese women, researchers said on Tuesday.

An obese woman who has weight-loss, or bariatric, surgery also may increase her chances of getting pregnant in the first place by normalizing her menstrual cycles and hormone levels, the researchers found.

Obese women are more likely to have difficulty getting pregnant, but after the surgery "there is some suggestion of increased fertility," Dr. Melinda Maggard, a surgeon and researcher at the Rand Corp think tank in Santa Monica, California, said in a telephone interview.

Bariatric surgery alters the digestive system's anatomy and reduces the volume of food that can be eaten and digested. The most common form is gastric bypass, which makes the stomach smaller and permits food to bypass part of the small intestine.

While losing weight naturally is preferable, weight-loss surgery does reduce the risks of pregnancy-related problems such as diabetes and high blood pressure that can harm the mother and her newborn, said the RAND researchers who analyzed data from 75 earlier studies.

The risks of premature delivery, having a low birth weight baby, or delivering an exceedingly large-bodied baby were reduced for women who had bariatric surgery compared to obese women, the report published in the Journal of the American Medical Association said.

In some cases, pregnancy-related risks after surgery were comparable to those for normal-weight women.

Bariatric procedures have surged in the past decade, with more than 200,000 performed last year in the United States. In the years 2002 to 2005 covered by the study, 150,000 U.S. women of child-bearing age underwent the surgery.

The study was requested by a group representing obstetricians and gynecologists.

A few women who had procedures that shrank the size of the stomach with bands or staples had the devices removed after they became pregnant — either because of discomfort or out of choice.

Others experienced pregnancy complications that likely were related to the surgery such as bowel obstructions, but overall maternal and infant deaths did not rise significantly.

Ideally, women should wait a year after the surgery to get pregnant to let their bodies adjust, but Maggard said some got pregnant earlier without problems.

Even overweight women not morbidly obese who are having difficulty getting pregnant might qualify for bariatric surgery if other weight-loss efforts fail, but improving fertility ought not be the main reason to have the surgery, Maggard said.

A related concern after weight-loss surgery might be unplanned pregnancies, Maggard said, because their previous dose of oral contraceptives may not be absorbed adequately.

"They might consider barrier methods of birth control or other means," she said.