Maturity of Cumulus Oocyte Complex (COC) Predicts the Outcome of Art. ∼ Focus on Dysmature ∼

Cumulus oocyte complex (COC) at oocyte retrieval with assisted reproductive technology (ART) can be easily classified in a visual manner by its maturity. We have classified them into three categories, mature, immature, and dysmature, for more than ten years. Dysmature COC is thought to be taken from atretic follicles. Although the classification has been generally used for over three decades, there is little study to identify whether the maturity of COC affect the results of ART, such as fertilization rate, implantation rate, and pregnancy rate. In this study, we present that the maturity of COC can be used as an indicator to predict outcome of ART. We demonstrate that dysmature COC results in poor outcome of ART. The infertile patients who underwent in vitro fertilization (IVF) / intracytoplasmic sperm injection cycles between January 2014 and December 2017 and performed frozen / thawed embryo transfer (ET) by August 2018 participated in the study. After institutional review board approved the study and individual patients provided informed consent prior, 292 patients, 527 cycles are investigated. COCs at oocyte retrieval observed with a stereoscopic microscope were classified in three categories, mature (M group), immature (IM group), and dysmature (D group), then following fertilization rates, ET rates, and pregnancy rates of fresh ET cycles or frozen/thawed ET cycles were calculated. Statistical analysis was performed with Chi-square test. P < 0.05 were considered significant. The total number of COCs retrieved was 2924 (1611 M group, 939 IM group, and 374 D group). The fertilization rate per COC number was significantly higher in M group (63.6%), and lower in D group (36.9%). The rate of fresh ET per COC was significantly higher in M group (8.0%), and lower in D group (3.1%), and there was no pregnancy in D group with fresh ET cycles. The rate of the number of frozen embryos per COC was significantly higher in M group (42.4%), and lower in IM group (33.7%) and D group (19.5%). The pregnancy rate per thawed ET cycle was significantly higher in D group (38.9%) compared to M group (21.6%) and IM group (19.7%). The maturity of COC at oocyte retrieval may be used as an indicator to predict outcome of ART. Dysmature COC resulted in poor fertilization rate, ET rate and embryo freezing rate. But, frozen embryo from dysmature COC may not worse in pregnancy rate compared to those from mature COC.