"We found no statistically significant difference in the overall rates of major and minor malformations or chromosomal abnormalities between newborns in the two groups," says Dr. Tulandi. "Our findings indicate concerns about a link between letrozole and birth defects are unfounded. This is significant because it confirms that letrozole can indeed be used in the treatment of infertility without increasing risk to the fetus."
The study contradicts an earlier, much smaller study linking letrozole to increased rates of inherited malformations. This study led to widespread concern about the use of letrozole, a drug which has been widely used in the treatment of infertility in recent years.
"There were several methodological problems with the earlier study," says Dr. Tulandi. "For one thing, it compared the incidence of birth defects in children conceived spontaneously with that in children conceived through fertility treatments using letrozole. This is an apples-and-oranges comparison, because there are always fewer birth defects in children conceived spontaneously." The earlier study also compared different age groups between the control and treatment.
The new study by Dr. Tulandi, Dr . Robert Casper from Department of Obstetrics and Gynecology at the University of Toronto, and their co-authors examined a total of 911 babies whose mothers were treated for infertility with either letrozole or clomiphene citrate from 2001 to 2005. Five Canadian centres in Quebec and Ontario participated.