The drug letrozole appears to be more effective than the standard drug clomiphene for helping women with polycystic ovary syndrome to achieve pregnancy, according to a large study from a research network supported by the National Institutes of Health.
PCOS affects from 5% to 10% of reproductive age women and may be the most common cause of female infertility, the study authors wrote. With PCOS, the ovaries are enlarged and contain multiple small cyst-like structures. Women with PCOS may produce an excess of male hormones, which interferes with ovulation, according to a news release.
The researchers found that women treated with letrozole not only were more likely to ovulate than were women treated with the standard drug, clomiphene, but also were more likely to have a live birth. This study showed conclusively that for this group of patients, treatment with letrozole resulted in proportionately more live births than did treatment with clomiphene, Louis V. DePaolo, PhD, chief of NICHDs Fertility and Infertility Branch, said in the release.
The study, appearing July 10 in the New England Journal of Medicine, enrolled 750 infertile women with PCOS who were between 18 and 40 years of age, from February 2009 through January 2012. The women were assigned at random to receive either clomiphene or letrozole for five days, beginning on the third day of their menstrual cycle, for up to five monthly cycles. If the women failed to ovulate or if their test results indicated that they produced insufficient progesterone following ovulation, the researchers increased the dose of the drug the women were being treated with during the next monthly cycle. Women with test results indicating conception had occurred were followed until an ultrasound exam could confirm that a pregnancy had been established and throughout pregnancy until delivery.
Of the 374 women who received letrozole, 103 (27.5%) eventually had a live birth. Of the 376 women who received clomiphene, 72 (19.1%) experienced a live birth. The cumulative ovulation rate was higher for the letrozole group, with ovulation occurring 834 times in 1352 cycles, or 61.7% of the time. The women in the clomiphene group ovulated 688 times out of a total of 1425 cycles, or 48.3% of the time.
The study authors noted that one prior study suggested that letrozole might increase the risk of birth defects, but added that their study results do not support the earlier studys findings. Although their study did not uncover an increased risk of birth defects, the authors concluded that additional studies are needed to rule out whether letrozole could pose a similar or greater risk of birth defects than do other infertility treatments, according to the release.