The proportion of nuclear mature oocytes affects ooplasmic competence of metaphase-II in relation to implantation and live birth with ICSI

Abstract Research Question Although ooplasmic maturity has been studied for some time, it remains poorly defined. We aim to identify the competence of MII oocytes in terms of fertilization and embryo development while considering the proportional maturity of the retrieved cohort. Design Couples treated by ICSI between 1993 and 2017 comprising female partners ≤35 years old were included. Cycles were divided into four groups according to the proportion of MII oocytes at the time of retrieval: Optimal (76-100%), adequate (51-75%), partial (26-50%), and minimal (1-25%). Results A total of 7,672 ICSI cycles ( optimal : 4,838; adequate : 2,252; partial : 518; minimal oocyte maturity: 64) in which 95,667 MII oocytes were injected using ejaculated spermatozoa were included. The decreasing proportion of MII significantly lessened normal fertilization (2-pronuclei) (78% to 71%; P optimal group to 4% in the minimal group ( P =0.003). Implantation (33% to 17%; P P P Conclusions High proportion of immature sibling oocytes (GV, MI) in the retrieved cohort affects the fertilization rate and embryo developmental competence of the mature (MII) inseminated oocytes. These findings support the notion that in addition to nuclear maturity, ooplasmic and membrane maturity are required for embryo developmental competence of MII oocytes retrieved. These findings may provide guidance toward superovulation protocols aimed at achieving a greater proportion of MII oocytes leading to higher fertilization rates and better pregnancy outcomes.