Searching for the optimal number of oocytes to reach a live birth after in vitro fertilization: a systematic review with meta-analysis

Objective

To investigate the relationship between the number of oocytes and both the live birth rate (LBR) after fresh embryo transfer and the cumulative live birth rate (CLBR).

Evidence Review

The optimal number of oocytes necessary to expect a live birth after in vitro fertilization remains unclear. A systematic review with meta-analysis was performed, searching for studies published between January 2004 and March 2021. Two independent reviewers performed study selection and data extraction according to Cochrane methods. The mean-weighted threshold of optimal oocyte number was estimated from documented thresholds, followed by a one-stage meta-analysis on articles with documented or estimable relative risks.

Results

After reviewing 1,090 records, 102 full-text articles were assessed for eligibility. A total of 45 studies were available for quantitative syntheses. Twenty-two and 21 studies were included in the meta-analyses evaluating the relationship between the number of retrieved oocytes and LBR or CLBR, respectively. For LBR, most studies reported a plateau or a peak effect, corresponding to a weighted mean of 13.5 oocytes, and the pooled dose-outcome showed a nonlinear relationship, with a plateau or even a drop beyond 15 oocytes. The meta-analysis of the relationship between the number of oocytes and CLBR found a nonlinear relationship, with a continuous increase in CLBR, including for high-oocyte yields.

Conclusion

Above a 15-oocyte threshold, LBR after fresh transfer plateaus, advocating for a freeze-all strategy. In contrast, the continuous increase in CLBR suggests that a strong response to controlled ovarian stimulation seems unlikely to impair oocyte quality. High numbers of oocytes could be offered to improve the chances of cumulative live births, after evaluating the benefit–risk balance.