Maximizing number of oocytes retrieved increases number of 2PNs, blastocysts, and cumulative live birth rates, without impairing primary transfer live birth rates

Objective: To investigate the association between the number of oocytes retrieved during ovarian stimulation and 2PNs, blastocysts, cumulative live birth rate (CLBR), and primary transfer live birth rate (PT-LBR).

Materials and Methods: We analyzed 365,473 autologous, non-cancelled retrieval cycles from 2014-2019 in the Society for Assisted Reproductive Technology Clinical Outcomes Reporting System (SART CORS). The relationships between the number of oocytes retrieved and the number of 2PNs and total blastocysts (number of blastocysts frozen plus transferred) were assessed using Pearson correlation. The CLBR was calculated per retrieval cycle, defined as at least one live birth from all linked embryo transfers. The PT-LBR was calculated per embryo transfer, defined as a live birth from the first embryo transfer associated with each retrieval cycle. The PT-LBR was stratified by fresh transfers (n = 230,708), frozen transfers without PGT (n = 42,209), and frozen transfers with PGT (n = 74,622). All results were calculated for 10 different quantiles of oocytes retrieved.

Results: Across all retrieval cycles, there was a positive linear correlation between oocytes and 2PNs (r = 0.86, p<0.01) and between oocytes and blastocysts (r = 0.85, p<0.01). The CLBR per retrieval cycle increased with oocyte yield. Sub-analyses of CLBR by different AMH and age groupings revealed similar increasing trends. The PT-LBR per attempted embryo transfer increased with the number of oocytes until approximately 15 oocytes, at which point it began to plateau.

Conclusions: Previous studies have suggested that retrieval cycles with high yields above 10-15 oocytes may be detrimental to live birth outcomes. Using the SART CORS dataset, we found that maximizing the number of oocytes is associated with higher CLBR, even in high-yield patients, and does not appear to impair oocyte quality or reduce PT-LBR. We note that our estimates of CLBR are conservative because we assumed that unused frozen embryos had zero probability of live birth.

Impact Statement: For patients undergoing ovarian stimulation, maximizing the number of oocytes retrieved is associated with increased 2PNs, blastocysts, and CLBR.