Clinical outcomes of frozen embryo transfer cycles after freeze-all policy to prevent ovarian hyperstimulation syndrome

To compare the clinical pregnancy rate (CPR) and ongoing pregnancy rate (OPR) in frozen embryo transfers (FETs) following either freeze-all policy to prevent ovarian hyperstimulation syndrome (OHSS; freeze-all group) or excess embryo cryopreservation after fresh embryo transfer (surplus group). The freeze-all group comprised 44 FET cycles performed in 25 women between 2010 and 2016. The surplus group comprised 53 FET cycles performed in 47 women during the same period. The cumulative CPR and OPR according to duration of cryopreservation (interval between cryopreservation and FET) was estimated using Kaplan-Meier plots. Cox regression analysis was used for identifying factor to affect to cryopreservation duration in cycles with pregnancy. In day 2-4 transfer cycles, the crude CPR (40% vs. 18.2%) and OPR (20% vs. 4.5%) were similar between the 2 groups. In day 5 transfer, the crude CPR (33.3% vs. 38.7%) and OPR (33.3% vs. 29%) were also similar between the 2 groups. The cumulative CPR (100% vs. 47.5%) and OPR (100% vs. 33.3%) in day 2-4 transfer as well as the cumulative CPR (46.7% vs. 100%) and OPR (46.7% and 74.8%) in day 5 transfer were also similar between the 2 groups. The median duration of cryopreservation was significantly shorter in the freeze-all group than in the surplus group (19.8 vs. 36.9 weeks, =0.04). Previous history of delivery was the only factor associated with a shorter cryopreservation duration in cycles with pregnancy (hazard ratio, 0.18; 95% confidence interval, 0.05-0.65; =0.01). Freezing embryos to prevent OHSS and transferring the frozen embryos later may guarantee an acceptable reproductive outcome.