Clinical pregnancy rates among anovulatory and oligoovulatory women after letrozole versus hormone replacement therapy in frozen-thawed embryo transfer cycles.

This cohort study investigated whether letrozole versus hormone replacement therapy (HRT) results in higher live birth rate among anovulatory and oligoovulatory women in frozen-thawed embryo transfer (FET) cycles. It was conducted from 1st February 2018 to 31st January 2019 and included 261 anovulatory and oligoovulatory women. Since letrozole has become an effective alternative to HRT cycles, 121 patients received letrozole in 121 cycles from 1st February 2018 to 31st January 2019 and were compared to 140 HRT FET cycles among 140 women from 1st February 2017 to 31st January 2018. The primary outcome was live birth rate. Secondary outcomes were clinical pregnancy, multiple pregnancy and miscarriage rates. Clinical pregnancy and live birth rates of transferred cleavage embryos were higher in the letrozole compared to the HRT group (36/65 (55.3%) vs. 20/110 (18.1%),  < 0.001) and (25/65 (38.4%) vs. 17/110 (15.4%),  < 0.001) respectively, whilst these rates were similar for transferred blastocyst embryos. Miscarriage and multiple pregnancy rates were similar between groups. The letrozole group was older than the HRT group (31.8 ± 5.1 vs. 29.9 ± 5.1 years,  = 0.002) and more smoked cigarettes ( = 0.035). Groups were similar regarding BMI, male versus non-male indication for fertility treatment, peak oestradiol levels, and numbers of oocytes retrieved, blastocysts, frozen and transferred embryos. Letrozole compared to HRT might improve live birth and clinical pregnancy rates among anovulatory and oligoovulatory women undergoing FET cycles.