Oct. 16 (HealthDay News) -- Women who become obese -- a step above overweight -- by the age of 18 are more likely to become infertile and develop polycystic ovarian syndrome than others, new research suggests.

These obese young women also less likely to become pregnant than women who become obese when they're older, according to the results of a study of 1,538 patients who were undergoing bariatric surgery at clinics in the United States. The women completed surveys about their medical and sexual histories.

Overall, however, the women in the study, who ranged in age from 18 to 78 years, were as likely to have been pregnant and to have given birth to at least one live child as women in the general population. Seventy-nine percent of those who took part in the study had been pregnant at least once, and 74 percent had at least one live birth, the researchers found.

About half of the study participants aged 18 to 44 who could become pregnant said they wouldn't try to have more children after bariatric surgery. The women in this group hadn't reached menopause and weren't sterilized, didn't have partners who were sterilized, and didn't have some other obstacle in the way of pregnancy.

However, 30 percent of the women who could still become pregnant stated that pregnancy was very important to them, and one-third of this group planned to get pregnant within two years of undergoing bariatric surgery, the study authors noted.

"As the incidence of obesity increases in the United States, women's health care practitioners are likely to care for a substantial number of patients who will undergo bariatric surgery. Studies like this one are extremely useful to help us determine how to advise these patients and best meet their needs," said Dr. William Gibbons, president-elect of the American Society for Reproductive Medicine, in a news release from the society.

The study findings appeared in the Oct. 7 online edition of the journal Fertility and Sterility.

SOURCE: American Society for Reproductive Medicine, news release, Oct. 8, 2009