Correlation of IVF outcomes and number of oocytes retrieved: a UK retrospective longitudinal observational study of 172 341 non-donor cycles

OBJECTIVE: How do numbers of oocytes retrieved per In vitro fertilisation (IVF) cycle impact on the live birth rate (LBR) and multiple gestation pregnancy (MGP) rates? DESIGN: Retrospective observational longitudinal study. SETTING: UK IVF clinics. POPULATION: Non-donor IVF patients. MAIN OUTCOME MEASURES: LBR per IVF cycle and MGP levels against number of oocytes retrieved into subgroups: 0, 1–5, 6–15, 16–25, 26–49 oocytes and 50+ oocytes. Relative risk (RR) and 95% CIs were calculated for each group against the intermediate responder with ‘6–15 oocytes collected’. RESULTS: From 172 341 attempted fresh oocyte retrieval cycles, the oocyte retrieved was: 0 in 10 148 (5.9%) cycles from 9439 patients; 1–5 oocytes in 42 574 cycles (24.7%); 6–15 oocytes in 91 797 cycles (53.3%); 16–25 oocytes in 23 794 cycles (13.8%); 26–49 oocytes in 3970 cycles (2.3%); ≥50 oocytes in 58 cycles (0.033%). The LBRs for the 1–5, 6–15, 16–25 and 26–49 subgroups of oocytes retrieved were 17.2%, 32.4%, 35.3% and 18.7%, respectively. The RR (95% CI) of live birth in comparison to the intermediate group (6–15) for 1–5, 16–25 and 26–49 groups was 0.53 (0.52 to 0.54), 1.09 (1.07 to 1.11) and 0.58 (0.54 to 0.62), respectively. The corresponding MGP rates and RR were 9.2%, 11.0%, 11.4% and 11.3%, respectively and 0.83 (0.77 to 0.90), 1.04 (0.97 to 1.11) and 1.03 (0.84 to 1.26), respectively. CONCLUSION: There was only limited benefit in LBR beyond the 6–15 oocyte group going to the 16–25 oocytes group, after which there was significant decline in LBR. The MGP risk was lower in 1–5 group.