Embryos derived from delayed mature oocyte should be cryopreserved and are favourable to transfer in a following endometrium synchronize frozen-thawed cycle.

Oocytes eligible for intracytoplasmic sperm injection (ICSI) are those that have progressed through meiosis to metaphase 2 (MII). The remaining delayed mature oocytes can be injected, aiming to achieve more embryos and a better chance to conceive. We aimed to assess the outcome of delayed matured oocytes, derived from either germinal vesicles or metaphase 1 (MI), that reached maturity (MII) 24 h following retrieval. The study population consisted of 362 women who underwent 476 IVF cycles. While fertilization rates were comparable between the sibling delayed mature oocyte group compared with injection on day 0 group (58.4% vs 62%, respectively, P = 0.07), the top-quality embryo rate per injected MII day 0 oocyte was significantly higher compared with day 1 injected oocyte (57.5% vs 43.9% respectively, P < 0.001). Moreover, following fresh transfer of embryos derived from delayed mature oocytes, implantation rate and the clinical pregnancy (CPR) and live-birth rates (LBR) per transfer were 3.9%, 3.3% and 1.6% respectively. When considering the following thawed embryo transfer cycles, implantation, pregnancy and LBR were non-significantly higher (10%, 8.3% and 8.3%, respectively). Although clinical outcomes are significantly lower when using embryos derived from delayed mature oocyte to mature day 0 oocytes, the additional embryos derived from delayed mature oocytes might contribute to the embryo cohort and increase the cumulative live-birth rate per retrieval. Moreover, the embryos derived from delayed mature oocyte favour a transfer in a frozen-thawed cycle rather than in a fresh cycle.