IMPORTANCE: Excess cryopreserved embryos present financial, logistical, and ethical constraints on patients and fertility clinics that are further complicated by the recently evolving US judicial landscape that may alter the legal status of frozen embryos and limit disposition options. It is therefore important to consider limiting the number of supernumerary embryos created from fresh donor oocytes. OBJECTIVE: To determine the optimal number of fresh donor oocytes to fertilize to achieve 1 live birth while minimizing supernumerary blastocysts. DESIGN, SETTING, AND PARTICIPANTS: This cohort study used data from recipients of fresh donor oocytes at member clinics of the Society for Assisted Reproductive Technology Clinic Outcomes Report System (SART CORS) between January 1, 2016, and December 31, 2020. Data were analyzed between August 2023 and June 2024. MAIN OUTCOMES AND MEASURES: The number of supernumerary blastocysts for a given number of fresh donor oocytes retrieved. RESULTS: There were 9395 fresh donor oocyte recipients included. The median (IQR) oocyte donor age at oocyte retrieval was 26 years (24-28 years), and the median (IQR) patient age at cycle start was 42 years (38-45 years). The median (IQR) number of oocytes retrieved was 20 (14-28), fertilized oocytes (2 pronuclei [2PN]) was 11 (7-17), usable embryos was 6 (3-10), and supernumerary blastocysts was 5 (2-8). When patients were divided evenly into quartiles based on the number of fresh donor oocytes retrieved (14 or fewer, 15 to 20, 21 to 28, 29 or more), it was associated with a significant increase in the number of cryopreserved supernumerary blastocysts (median [IQR] blastocysts by quartile: 2 [1-4] vs 4 [2-7] vs 6 [3-9] vs 9 [4-14], respectively; P < .001). However, the live birth rate was lower only for those in the first quartile receiving 14 or fewer oocytes (50.8% [1207 of 2376] vs 64.1% [1497 of 2336] vs 67.9% [1631 of 2401] vs 67.9% [1550 of 2282]; P < .001). CONCLUSIONS AND RELEVANCE: In this retrospective cohort study of fresh donor oocyte cycles, the number of supernumerary blastocysts to achieve 1 live birth for a given number of fresh donor oocytes exposed to sperm was approximated, which may be valuable for counseling patients.