OBJECTIVE What is the optimal number of frozen donor oocytes to thaw and fertilize to achieve one live birth while minimizing supernumerary embryos? CONCLUSIONS For patients who want only one child, fertilizing 6-7 frozen donor oocytes would result in approximately one supernumerary embryo while maintaining the live birth rate. BACKGROUND Studies on frozen donor oocyte outcomes focus on live birth rate, but little is known about the resulting number of supernumerary embryos. METHODS This is a retrospective cohort study using data from the 2016-2020 Society for Assisted Reproductive Technology Clinic Outcomes Reporting System. A total of 11,554 frozen donor oocyte recipients undergoing their first cycle with frozen donor oocytes were included. METHODS The 11,554 frozen donor oocyte recipients were stratified into quartiles based on the number of frozen donor oocytes thawed (<6, 6, 7, and >7). The primary outcome was the number of supernumerary blastocysts, defined as the number of blastocysts remaining after the first live birth, or at the final transfer cycle if the patient did not have a live birth. RESULTS On average, patients thawed 6.74 ± 1.96 oocytes, resulting in 4.77 ± 2.07 2PNs (2 pronuclei), 2.44 ± 1.59 usable embryos, and 1.02 ± 1.47 supernumerary blastocysts. The average number of cryopreserved supernumerary blastocysts increased as the number of frozen donor oocytes thawed increased (0.50 vs. 0.90 vs. 0.99 vs. 1.49 blastocysts in each quartile, respectively, P<0.01). However, live birth rates were only significantly lower when less than six frozen donor oocytes were thawed and fertilized (37.6% vs. 48.5% vs. 50.3% vs. 51.3%, P<0.01). CONCLUSIONS There are limitations to utilizing national databases, including missing data and the inability to extrapolate additional nuanced information not originally collected. CONCLUSIONS The number of supernumerary blastocysts increases even with small increases in the number of frozen donor oocytes exposed to sperm. While thawing 6-7 frozen donor oocytes aligns with most practices, almost a quarter of patients thawed more than 7 frozen donor oocytes, which led to a significant increase in the number of supernumerary embryos to 1.49 without a significant increase in live birth rate. BACKGROUND Xiaoyue Ma, MSc is partially supported by the following grant: Clinical and Translational Science Center at Weill Cornell Medical College (1-UL1-TR002384-01). Steven Spandorfer is a former President of the Society for Assisted Reproductive Technology. BACKGROUND Not applicable.