Age-specific blastocyst conversion rates in embryo cryopreservation cycles

What is the blastocyst conversion rate in embryo cryopreservation cycles, per year of female age?

Retrospective cohort study including patients undergoing their first ovarian stimulation cycle at our center with planned freeze-all strategy January 1st, 2014-June 30th, 2020. Primary outcome was blastocyst conversion rate. Secondary outcomes included mature oocyte and fertilization rates. Patients were stratified by year of age to assess oocyte yield and embryo development outcomes.

3,362 patients were included. The median blastocyst conversion rate in patients ≤30 was 66.7% (interquartile range 50.0-86.6) and remained statistically comparable through age 40 with a significant decline among ages ≥41 (41-years: marginal effect (ME) -5.2% (-9.7 to -0.7); 42-years: ME -9.6% (-14.3 to -4.8); 43-years: ME -7.7% (-12.8 to -2.6); ≥44-years: ME -20.8% (-26.5 to -15.1)). For the entire cohort, the median mature oocyte rate was 81.8% and the median fertilization rate was 81.8%. The mature oocyte and fertilization rates remained statistically comparable for each year of age except age ≥44 which had a statistically significantly increased mature oocyte rate (ME 4.4% (1.3 to 7.5)) and statistically significantly decreased fertilization rate (ME -5.8% (-9.8 to -1.9)) CONCLUSIONS: In embryo cryopreservation cycles, the blastocyst conversion rate remained statistically comparable through age 40 followed by a statistically significant decline for patients ≥41; however, the mature oocyte and fertilization rates were not impacted by increasing age until age ≥44. Even in women ≥44, over 40% of fertilized oocytes developed to blastocyst. Overall, this information is useful when counseling patients during the embryo culture stage regarding predicted blastocyst yield.