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Research question: What is the optimal number of oocytes retrieved at which maximum live birth rate is observed after fresh autologous assisted reproductive technology (ART) cycles for women of different ages? Design: Retrospective cohort study of all fresh autologous ART aspiration cycles (n = 256,643) undertaken in Australia and New Zealand between 2009 and 2015. Primary outcome measure was live birth rate (LBR) (delivery of at least one liveborn baby at 20 weeks’ gestation or over per fresh aspiration cycle). Cycles were grouped according to female age (<30, 30–34, 35–49, 40–44 and ≥45 years) and ovarian response (one to three, four to nine, 10–14, 15–19, 20–25 and ≥25 oocytes). Secondary outcome was incidence of ovarian hyperstimulation syndrome (OHSS) requiring hospitalization. Results: At different oocyte yields, LBR per fresh aspiration cycle peaked and then declined at, depending on female age: <30 years: six to 11 oocytes (LBR 31–34%); 30–34 years: 11–16 oocytes (LBR 29–30%); 35–39 years: nine to 17 oocytes (LBR 21–24%); and 40–44 years: 15–17 oocytes (LBR 11–12%). The incidence of OHSS increased significantly with the number of oocytes retrieved, from 1.2% with 15 oocytes retrieved to 9.3% with 30 or more oocytes retrieved (P < 0.001). Conclusion: The optimal number of oocytes at which maximum LBR was observed in a fresh aspiration cycle was highly dependent on age. Because of the observational nature of the results, a cause–effect relationship between the number of oocytes retrieved and LBR should not be assumed; evidence from well-designed randomized control trials is required before clinical advice can be suggested.

The association between the number of oocytes retrieved and fresh live birth rate (LBR) or cumulative LBR (CLBR), and whether an optimal number of oocytes are retrieved when LBR or CLBR are maximized, are highly relevant clinical questions; however published results are conflicting. A systematic review of all eligible studies (n = 16) published until January 2020 on MEDLINE, Embase, Scopus, CINAHL and Web of Science was conducted. Five studies evaluated only LBR from fresh cycles, five studies evaluated only CLBR from stimulated cycles and six evaluated both. A marked difference was observed between the oocyte yields at which LBR and CLBR were reportedly maximized in the individual studies. On the basis of nine studies, the optimal number of oocytes at which fresh LBR seems to be maximized is proposed to be between 12 and 18 oocytes (15 oocytes was the most common suggestion). On the other hand, CLBR continues to increase with the number of oocytes retrieved. This is the first systematic review on the topic, and it suggests that the retrieval of 12–18 oocytes is associated with maximal fresh LBR, whereas a continuing positive association is present between the number of oocytes retrieved and CLBR.