A common strategy for treating infertility in women with polycystic ovary syndrome may actually reduce their chances of pregnancy, a new study suggests.

In the study, some women with PCOS were given progestin as a first step in their infertility treatment. Progestin, which is a synthetic form of the hormone progesterone, leads to a thickening in the lining of the uterus, and is sometimes administered before fertility drugs to women with PCOS who wish to become pregnant.

However, women who skipped the progestin treatment before receiving fertility drugs were four times more likely to conceive than women given progestin. Ultimately, 20 percent of the women who did not receive progestin gave birth, compared with about 5 percent of the women who received progestin, the researchers said.

“Our results indicate that a treatment with progestin before ovulation induction is counterproductive in helping women with PCOS achieve pregnancy,” said study researcher Dr. Esther Eisenberg, of the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Ovulation induction refers to the drugs given to stimulate the release of an egg.

Polycystic ovary syndrome is a disorder in which the ovaries, and sometimes the adrenal glands, produce excess amounts of hormones known as androgens. Women with PCOS typically have menstrual irregularities, and may have difficulty getting pregnant. As many as 5 million U.S. women have the condition, according to the Department of Health and Human Services.

The study, which involved more than 600 women with PCOS, was published online this month in the journal Obstetrics and Gynecology. It was funded by the National Institutes of Health.

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