Embryo attrition in planned PGT-A: predicting the number of available blastocysts for transfer

During a typical IVF cycle, there is unavoidable attrition from oocytes retrieved to blastocysts formed. Some patients will not have blastocysts available to biopsy or embryos for transfer. The purpose of this study was to predict the number of transferable blastocysts available for patients based on their age and number of 2pn zygotes.

This was a retrospective cohort study of all fresh autologous IVF and ICSI cycles in which PGT-A was planned from 1/2012 to 3/2020. In total, 746 cycles from 571 patients were analyzed. Patient cycles were stratified into two groups: less than four 2pn zygotes (n = 85) and at least four 2pn zygotes (n = 661). Cycles were then stratified by patient age. Cycle outcomes, including number of cleavage-stage embryos, blastocysts, euploid blastocysts, and low level mosaic blastocysts, were determined.

Cleavage-rate was independent of age and number of 2pn zygotes and ranged between 96 and 100%. Blastocyst conversion and euploid blastocyst conversion rates were directly correlated to age, ranging from 52 to 83% for blastocyst conversion and 0-28% for euploid blastocyst conversion. For patients above the age of 40 years with less than four 2pn zygotes, the risk of having no transferable embryos was 99.7%.

While the literature demonstrates higher live birth rates with the use of PGT-A in women of advancing age, this is inconsequential if there is no embryo available to transfer. Women over 40 years with less than four 2pn zygotes should consider transfer of one or more untested embryos either on day 3 or on day 5.