Letrozole, a prescription medication commonly used to suppress estrogen in women with hormone-responsive breast cancer, may prove beneficial for women undergoing frozen-thawed embryo transfer (FET), according to researchers. This off-label use is legal in the United States and the United Kingdom, but has been banned in other countries due to a perceived risk of birth defects. Research has shown letrozole poses lower risks of birth defects than clomiphene.

From Oct. 201o to Sept. 2012, more than 1,200 FET cycles were evaluated. In total, 713 cycles (354 HRT cycles and 359 letrozole cycles) were evaluated. Five hundred seventeen natural cycles were included as the control group.

Researchers reported clinically significant improvements in implantation rate (8% increase), clinical pregnancy rate (9% increase) and live birth rate (12% increase) when letrozole was used. There was no difference in rates when letrozole was compared with the natural cycle control group. Another positive result was the difference in abortion rates between the HRT group and letrozole group; 21% and 12%, respectively. Twin pregnancy and ectopic pregnancy rates were similar across all three groups.

Conclusion: Letrozole improves implantation rate, clinical pregnancy rate, live birth rate and abortion rate compared to HRT in FET. When letrozole results were compared with natural cycle results, the outcomes were similar. Letrozole appears to mimic natural cycle and reduce risk with FET.

Source: Song-jun Li, Yong-jing Zhang, Xiao-shan Chai, Mei-fang Nie, Yu-yan Zhou, Jian-lin Chen, Guang-shi Tao. Letrozole ovulation induction: an effective option in endometrial preparation for frozen–thawed embryo transfer. Archives of Gynecology and Obstetrics. October 2013. DOI: 10.1007/s00404-013-3044-0.