Intrapatient variability in the number of retrieved oocytes and ovarian response categories between consecutive in vitro fertilization cycles

OBJECTIVE: To examine intrapatient variability in retrieved oocyte numbers across consecutive in vitro fertilization (IVF) ovarian stimulation (OS) cycles with an identical OS protocol. DESIGN: Cross-continental, multicenter retrospective cohort study. SUBJECTS: Patients undergoing OS for IVF (2014-2024) with ≥2 OS cycles within 6 months using the same OS protocol, gonadotropin type, and initial and daily dose; all underwent freeze-all-cycles and had ≥1 oocyte retrieved in each of the two consecutive cycles. For each patient, the earliest consecutive pair meeting criteria was analyzed. EXPOSURE: Oocyte yield in the first vs. consecutive OS cycle. MAIN OUTCOME MEASURES: Primary outcomes included: (i) average percentage change in oocyte yield between cycles (higher divided by lower oocyte yield); and (ii) 25th, 50th (median), and 75th percentiles of oocyte-yield percentage change, overall and by age groups (≤30, 31-35, 36-39, ≥40 years). Secondary outcomes included: (i) coefficient of determination (R2) between each cycle's oocyte count and the patient's average oocyte count across both cycles, representing the extent of variation explained by the patient's baseline profile; (ii) shifts between ovarian response categories, poor (1-3 oocytes), suboptimal (4-9), normal (10-14), and hyper-response (≥15); (iii) average and median percentage change in mature-oocyte yield. RESULTS: Overall, 801 cycle pairs met the inclusion criteria. Mean daily gonadotropin dosage was 361.5 ± 112.6 IU; with comparable demographic and cycle characteristics between cycles. Overall, the average percentage change in oocyte yield was 62.7%; the 25th, 50th (median), and 75th percentiles were 16.7%, 40%, and 80%, respectively. Fifty-percent of patients showed >33% difference in retrieved oocytes, and 381/801 (47.57%) shifted ovarian response categories, with 29/381 (7.61%) shifting across two categories. Median oocyte yield percentage change was 44.4% in women ≥40 vs. 33.3% in those ≤30 years. The coefficient of determination between each cycle and the average of the two cycles was 0.834, representing the optimal performance any prediction model could achieve when predicting oocyte yield given baseline characteristics alone. The average percentage change in mature oocyte yield was 74.5%, with a median of 50%. CONCLUSION: Cycle-to-cycle variations in retrieved oocyte yield exist despite the same cycle conditions, across all age groups, reflecting fluctuations in ovarian follicular readiness and response, challenging ovarian response categorization based on oocyte yield and stressing the importance of key performance indicators in IVF OS cycles.