Be careful what you inject, as late maturing ooocytes only abate your rates: developmentally young oocytes are not ready for the needle!

Intracytoplasmic sperm injection (ICSI) of normally mature MII oocytes (NMO) at ∼4hr post retrieval is the standard of care, however some centers also ICSI late maturing oocytes (LMO) that were not mature at the time of hyaluronidase (∼2.5hr post retrieval) but have subsequently matured to MII at the time of ICSI. Development delay of oocyte maturation post retrieval may be due to many factors that could influence the fertilization and developmental potential of oocytes. Our study investigated 6713 cycles and their individual oocytes maturation history, comparing laboratory and clinical data. Retrospective analysis. Fresh ICSI cycles (2002-12) were classified into 6366 (94.8%) cycles with only NMO injected and 347 (5.2%) in which LMO were also/only injected. Embryo transfers were classified as having either No or ≥1 LMO derived embryo. Statistical analysis was performed by χ2, with significance at P<0.05. Significant decreases in fertilization and implantation were found in cycles that had LMO and decreased further when only LMO oocytes were available for injection.Tabled 1LMO at ICSINo≥1OnlyFertilization72%*,∼58%*52%∼LMO at ETNo≥1OnlyImplantation29%+,^19%+5%^*,∼,+P<0.01; ^P=NS due to sample size. Open table in a new tab *,∼,+P<0.01; ^P=NS due to sample size. Following the individual oocytes in LMO cases also demonstrated LMO had decreased fertilization (64% vs 41%: P<0.01) and implantation (26% vs 15%: P=NS due to sample size). Our study demonstrated the highest fertilization and implantation with oocytes that were NMO at the time of hyaluronidase. When LMO were injected, they had decreased fertilization (which was demonstrated as the absence of a 2PN at 18hrs and not increased abnormal fertilizations), and the transfer of LMO derived embryos showed decreased implantation rates. The injection of LMO should be performed with caution as we have demonstrated their clinical potential is significantly limited, suggesting that though they appear morphologically normal, they could be reproductively compromised.