Reassessing the impact of letrozole co-administration in controlled ovarian hyperstimulation: findings from a single-center repeated measures study

Purpose To explore whether letrozole improved outcomes in subsequent controlled ovarian hyperstimulation (COH) cycles. Methods This was a retrospective repeated measures cohort study examining COH cycles. Patients were included if they underwent two cycles for unexplained infertility, male factor infertility, or planned oocyte/embryo cryopreservation. The first cycles for all patients implemented a non-letrozole, conventional gonadotropin protocol. Second cycles for the study group included letrozole (2.5–7.5 mg for 5 days) with no medication change to second cycles amongst controls. Our primary objective was to compare oocyte yield. Cohorts were then subdivided by pursuit of oocyte (OC) or embryo (IVF) cryopreservation. Secondary outcome amongst the OC subgroup was oocyte maturation index (metaphase II (MII)/total oocytes). Secondary outcomes amongst the IVF subgroup were normal fertilization rate (2-pronuclear zygotes (2PN)/oocytes exposed to sperm), blastocyst formation rate (blastocysts/2PNs), and embryo ploidy (%euploid and aneuploid). Results Fifty-four cycles ( n = 27) were included in letrozole and 108 cycles ( n = 54) were included in control. Oocyte yield was higher in second cycles ( p