Polycystic ovary syndrome -- the most common cause of female infertility in the United States -- causes higher than normal levels of the male hormone androgen, infrequent periods and small cysts on the ovaries. It affects 5 to 10 percent of reproductive-age women, according to background information in the study.
Currently, doctors typically prescribe clomiphine (Clomid) to boost fertility for women with polycystic ovary syndrome. However, this new study suggests the drug letrozole (Femara) results in better ovulation, conception and birth rates.
"We found a simple and comparatively safe and vastly more effective treatment for [polycystic ovary syndrome]," said lead researcher Dr. Richard Legro, a professor of obstetrics and gynecology at Penn State University's College of Medicine in Hershey, Penn.
Clomiphine, which works by stimulating ovulation, has been the standard treatment for years, but has a high rate of multiple births, Legro said.
Letrozole, a treatment for breast cancer in postmenopausal women, works by blocking estrogen production, tricking the ovaries into producing more of the hormone, he explained.
The new study, funded by the U.S. National Institutes of Health, was published July 10 in the New England Journal of Medicine.
Researchers found that almost 28 percent of the women taking letrozole had babies after five cycles, compared with about 19 percent of those taking clomiphene.
Also, women taking letrozole had fewer twin pregnancies, compared with those taking clomiphene -- about 3 percent versus 7 percent, the study found.
"Clomiphine may be trumped," Legro said. "To see a 40 percent improvement in birth rate is a huge difference."
Whether letrozole will cause more birth defects than other drugs isn't known, Legro said. "We will need other studies to show that the rates of birth defects are actually low -- lower than we would expect in an infertile population," he said.
Letrozole, a generic drug, is relatively inexpensive. Thirty pills cost around $56, similar to the cost of clomiphene, Legro said. "This is an affordable form of infertility treatment," he said.
Dr. Avner Hershlag, an infertility specialist at the North Shore-LIJ Health System in Manhasset, N.Y., said the new study confirms earlier observations. The findings show that letrozole is not only appropriate for patients with polycystic ovaries, but that it is also associated with higher live birth rates and ovulation rates, he said.
Hershlag said he prescribes both letrozole and clomiphene for patients. "The decision to use one or the other depends on several factors, including insurance coverage and cost," he said.
For the study, Legro's team randomly assigned 750 women with polycystic ovary syndrome to take clomiphene or letrozole. The drugs were given in five menstrual cycles with the dosage increased with each cycle.
The overall ovulation rate was higher with letrozole than with clomiphene -- 62 percent compared to 48 percent.
Clomiphene was associated with hot flashes, while some women using letrozole reported fatigue and dizziness. For both drugs, birth defects were rare and rates were similar. They were comparable with those seen in studies of women who conceive without treatment, Legro said.
For more about polycystic ovary syndrome, visit the U.S. Department of Health and Human Services.