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NIH Research Matters

February 19, 2007

Established Drug Bests Newcomer in Treating Female Infertility

Researchers report that a common cause of female infertility is better treated with an established ovulation-inducing drug than with an increasingly popular alternative. The new study is the largest, most comprehensive effort to date comparing the two drugs' abilities to promote pregnancy in women with polycystic ovary syndrome (PCOS), a hormonal disorder often marked by infertility

A young woman smiling

PCOS affects about one in 15 women in the U.S. The disorder is characterized by high levels of male hormones, which can interfere with ovulation and cause the ovaries to become enlarged and packed with fluid-filled sacs, or cysts. Symptoms include irregular menstrual periods, excessive body and facial hair, acne, obesity and infertility.

For decades, physicians have treated PCOS-related infertility with the ovulation-stimulating drug clomiphene. But clomiphene also increases the likelihood of twins or other multiple pregnancies. In searching for alternatives, researchers noted that PCOS is often associated with a prediabetic condition known as insulin resistance, which can be improved by the diabetes drug metformin. Several small clinical trials have since shown that metformin can boost ovulation in women with PCOS. The current study asked whether metformin treatment can result in more pregnancies and live births without increasing the likelihood of multiple pregnancies

Researchers randomly assigned 626 infertile women with PCOS to receive one of three treatments—clomiphene, metformin or a combination of the two—for up to six months. The study was conducted by the Reproductive Medicine Network, a multi-center research network funded by NIH's National Institute of Child Health and Human Development (NICHD), with additional support from NIH's National Center for Research Resources (NCRR).

The findings appeared in the February 8, 2007, issue of the New England Journal of Medicine. Compared to the women who received metformin alone, those in either of the groups taking clomiphene were at least three times more likely to give birth. The birth rates were 7.2% with metformin, 22.5% with clomiphene and 26.8% with the clomiphene-metformin combination therapy, although the difference between the latter two wasn't large enough to rule out the possibility that it was due to chance. As expected, the two groups that received clomiphene, alone or with metformin, had more multiple pregnancies: 6.4% with clomiphene only, 3.3% with the combination therapy and none with metformin only.

Women in the combination therapy group had a significantly higher ovulation rate than those in the other two groups, although more ovulations didn't lead to significantly more pregnancies. “Our results show that you can't use ovulation as a surrogate for pregnancy,” said lead investigator Dr. Richard Legro of the Penn State College of Medicine. “An ovulation on clomiphene treatment is twice as likely to result in pregnancy as an ovulation on metformin, thus all ovulations are not alike.”

Legro and his colleagues say that this large clinical trial supports the use of clomiphene as a first-line infertility treatment for women with PCOS.

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Editor: Harrison Wein, Ph.D.
Assistant Editors: Vicki Contie, Carol Torgan, Ph.D.

NIH Research Matters is a weekly update of NIH research highlights from the Office of Communications and Public Liaison, Office of the Director, National Institutes of Health.

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This page last reviewed on December 3, 2012

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