Impact of blastocyst quality at time of cryopreservation on frozen embryo transfer (FET) success rates is dependent on patient age

Abstract

OBJECTIVE: Freezing high quality embryos does not affect implantation and pregnancy rates (Selick, 1995). Little has been reported on the impact of freezing poor quality embryos. The objectives were to evaluate the impact of freezing optimal (OP) versus suboptimal (SO) quality embryos on clincal pregnancy (CPR) and live birth rates (LBR) and to determine whether there is a differential effect based on patient age at FET. DESIGN: Retrospective data analysis of 518 FET cycles from 2001 to 2007. Patients were divided into two groups based on age at FET (<35 and ≥ 35) and two levels of prefreeze quality (OP ≥ CBB; SO <CBB). Only FETs where all embryos thawed were within the same prefreeze quality group were analyzed. MATERIALS AND METHODS: Blastocysts with inner cell mass grades A, B or C (A best, F worst) and trophoblast and cavity grades A or B (A best, D worst) were frozen 112-140 hours post-insemination using 2-step glycerol-sucrose. Embryos not meeting grading criteria were frozen by exception. Embryos were thawed using modified glycerol-sucrose. Outcomes were analyzed with Chi-square. RESULTS: Differences in CPR and LBR between the two age groups were less pronounced for OP (7%, 9%) than for SO (45%, 38%) embryos. Survival rates were similar between age groups for OP embryos, but appeared to be diminished for SO embryos for the older age group.Table 1Effect of blastocyst quality at cryopreservation and patient age at FET on CPR and LBR.NNo. ThawedNo. Survived (%)No. Pregnant ≥ 1FHB (%)No. Live Births (%)Optimal Quality<35257492426 (87)132 (51)120 (47)≥ 35228423361 (85)100 (44)86 (38)difference2% (NS)7% (p<0.01)9% (p<0.05)Suboptimal Quality<35163831 (82)11 (69)9 (56)≥ 35172718 (67)4 (24)3 (18)difference15% (p=0.17)45% (p<0.009)38% (p<0.02) Open table in a new tab CONCLUSIONS: These results suggest more stringent quality criteria may be required for blastocyst cryopreservation for women ≥ 35 to ensure a reasonable chance of pregnancy with FET.