LAUSR

To compare the effectivity of flexible-start medroxyprogesterone acetate (MPA) co-treatment ovarian stimulations (OS) with flexible-start gonadotropin-releasing hormone antagonist (GnRH-ant) co-treatment OS, in blastocyst freeze-all IVF cycles. This matched cohort study was performed at a single IVF center. Study cycles were extracted from freeze-all IVF cycles performed between February 2015 and June 2018 with cycles grouped according to the co-treatment protocol (MPA and GnRH-ant groups) used. MPA cycles were matched 1:1 using antral follicle count, female age, infertility duration, and female body mass index, with GnRH-ant cycles, resulting in 825 matched cycles. MPA or CET co-treatment was started when leading follicles reached 11–12 mm. Duration of OS was significantly longer, and total FSH dose was significantly higher in the MPA group. Numbers of mature oocytes retrieved were similar; however, the mature oocyte retrieval rate (83.8 vs. 97.1%; p < 0.001), number of blastocysts, blastocyst rate (36.4 vs. 41.4%; p < 0.001) and > 2 viable blastocyst rate were all significantly lower in the MPA group. The live birth (LB) per transfer rates (51.6 vs. 55.7%; p = 0.155) were similar; however, the LB rate per treatment was significantly lower (40.9 vs. 45.8%; p = 0.05). A linear regression included the OS co-treatment protocol (GnRH-ant; 1.4 (1.07-1.81); p = 0.013) in the final model to predict having > 2 viable blastocysts. Flexible-start MPA co-treatment OS was as effective in freeze-all IVF cycles as GnRH-ant co-treatment, with similar LB per transfer rates; however, increased cycle cancellation and reduced blastocyst numbers reduced LB per treatment rates significantly.