Abstract
Study question
To investigate the relationship between the number of oocytes and both the live birth rate after fresh embryo transfer and the cumulative live birth rate.
Summary answer
Above a 15-oocyte threshold, live birth rate (LBR) following fresh transfer plateaus, whereas a continuous increase in cumulative live birth rate (CLBR) is observed.
What is known already
Several lines of evidence indicate that number of oocytes represents a key point for in vitro fertilization (IVF) success. However, consensus is lacking regarding the optimal number of oocytes for expecting a live birth. This is a key question because it might impact the way practitioners initiate and adjust COS regimens.
Study design, size, duration
A systematic review and meta-analysis was performed. MEDLINE, EMBASE, and Cochrane Library were searched for studies published between January 01, 2004, and August 31, 2019 using the search terms: “(intracytoplasmic sperm injection or icsi or ivf or in vitro fertilization or fertility preservation)” and “(oocyte and number)” and “(live birth)”.
Participants/materials, setting, methods
Two independent reviewers carried out study selection, quality assessment using the adapted Newcastle-Ottawa Quality Assessment Scales, bias assessment using ROBIN-1 tools, and data extraction according to Cochrane methods. Independent analyses were performed according to the outcome (LBR and CLBR). 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.
Main results and the role of chance
After reviewing 843 records, 64 full-text articles were assessed for eligibility. A total of 36 studies were available for quantitative syntheses. Twenty-one and 18 studies were included in the meta-analyses evaluating the relationship between the number of retrieved oocytes and LBR or CLBR, respectively. Given the limited number of investigations considering mature oocytes, association between the number of metaphase II oocytes and IVF outcomes could not be investigated. Concerning LBR, 7 (35.0%) studies reported a plateau effect, corresponding to a weighted mean of 14.4 oocytes. The pooled dose-response association between the number of oocytes and LBR showed a non-linear relationship, with a plateau beyond 15 oocytes. For CLBR, 4 (19.0%) studies showed a plateau effect, corresponding to a weighted mean of 19.3 oocytes. The meta-analysis of the relationship between the number of oocytes and CLBR found a non-linear relationship, with a continuous increase in CLBR, including for high oocyte yields.
Limitations, reasons for caution
Statistical models show a high degree of deviance, especially for high numbers of oocytes. Further investigations are needed to assess the generalization of those results to frozen mature oocytes, especially in a fertility preservation context, and to evaluate the impact of female age.
Wider implications of the findings
Above a 15-oocyte threshold, LBR following fresh transfer plateaus, suggesting that the freeze-all strategy should probably be performed. In contrast, the continuous increase in CLBR suggests that high numbers of oocytes could be offered to improve the chances of cumulative live births, after evaluating the benefit–risk balance.
Trial registration number
Not applicable
Extended culture of day 3 embryos improves live birth rate in in vitro fertilization-embryo transfer
