In addition, fewer twin pregnancies occurred in the women who took letrozole -- 3.9 percent on letrozole and 6.9 percent on clomiphene.

Birth defects were rare and rates were similar between the two medications, comparable to those from studies of women who conceive without treatment, they noted.

"In conclusion, our study showed that letrozole was superior to clomiphene as a treatment for anovulatory infertility in women with the polycystic ovary syndrome," the researchers wrote in their paper.

But the researchers also noted that further study with larger numbers of infants is needed to clarify the safety and teratogenic risks with letrozole relative to those with other infertility therapies.