Embryonic, genetic and clinical outcomes of fresh versus vitrified oocyte: A retrospective cohort study

Objective: To compare embryonic development, ploidy status and clinical outcomes between fresh and frozen-thawed oocytes. Methods: This retrospective cohort study evaluated 83 fertilization cycles including both fresh and frozen oocytes from 79 patients at the HP Fertility Center of Hai Phong International Hospital of Obstetrics and Pediatrics in Vietnam. The patient underwent several ovarian stimulation cycles to accumulate a certain number of oocytes that would be vitrified. In the last oocyte retrieval, all patient's oocytes including both frozen and fresh would be fertilized. The outcomes included the rates of oocyte survival, cleavage embryo, blastocyst, ploidy status, pregnancy, biochemical pregnancy and clinical pregnancy. Results: The oocyte survival rate after thawing was 96.5%. No statistically significant difference was found when comparing fresh and frozen oocytes regarding fertilization rate (78.1% vs. 75.5%, P=0.461), usable cleavage embryo rate (86.9% vs. 87.2%, P=0.916) but usable blastocyst rate was found higher statistically in the frozen oocyte group (44.4% vs. 54.0%, P=0.049). The percentages of euploid, aneuploid and mosaic embryos between the fresh group and the vitrified group had no significant differences (33.8% vs. 31.6%, P=0.682; 51.0% vs. 54.2%, P=0.569; 15.2% vs. 12.4%, P=0.787; respectively). The rates of pregnancy, biochemical pregnancy and clinical pregnancy had no statistical difference (68.8% vs. 64.8%, P=0.764; 12.5% vs. 3.6%, P=0.258; 37.5% vs. 46.4%, P=0.565). 17 Mature oocytes are the minimum to have at least one euploid embryo. Conclusions: Oocyte vitrification does not affect embryonic, genetic and clinical results. The number of mature oocytes should be considered for fertilization in some cases.