Is Timing of Embryo Cryopreservation Important? – Comparison of Pregnancy Outcome of Blastocyst Embryo Transfers after Cryopreservation at Cleavage versus Blastocyst-Stage Embryos

Intro - During ART, embryos are cryopreserved to perform later frozen thawed embryo transfers. Some reports have shown that blastocyst transfer of thawed cleavage-stage embryos, that are cultured to blastocysts has better reproductive outcome than thawed blastocysts.

Aim - To compare reproductive outcome for blastocyst embryo transfers after cryopreservation of cleavage vs. blastocyst stage embryos.

Methods - This was a retrospective cohort of patients undergoing ART who had blastocyst transfer post thawing at cleavage-stage [TCS] (n=114) or thawing at blastocyst stage (TB) (n=97) in Hadassah Mount Scopus IVF unit during 2014-2016. We collected information regarding patient parameters, medical history, cause for infertility, COH protocol, MII oocytes number, embryo quality, implantation, pregnancy, and live birth rate.

Results – The mean number of high quality embryos 72h after fertilization before freezing was significantly higher in the TCS group (8.78±5.49 vs. 5.37±3.86, p<0.001). Yet, among 311 blastocysts transferred, there were more ≥3AA grade blastocysts in the TB group (17.2% vs 28.3%, p<0.0001). Blastocyst transfers post TCS yielded comparable pregnancy, implantation, and live birth rates. (37.6% vs. 28.2%, p=0.162; 23.8% vs. 20%, p=0.428; 22.9% vs. 19.6%, p=0.563).

Conclusions - Reproductive outcome for blastocyst embryo transfers after cryopreservation at either cleavage vs. blastocyst stage is comparable and irrespective of the number of high quality embryos at cleavage stage.