Effects of two vitrification protocols on the developmental potential of human mature oocytes

The aim of the present study was to compare an 'open' vitrification protocol to a 'closed' vitrification protocol for mature human oocytes. A prospective comparison between fresh and sibling vitrified oocytes and a retrospective comparison between the two vitrification protocols were performed. For recruited patients undergoing an IVF cycle, two or three fresh oocytes were inseminated with intracytoplasmic sperm injection (ICSI) and the remaining three or more oocytes were vitrified according to manufacturer's instructions with a 'closed' or an 'open' vitrification system. After an unsuccessful fresh cycle, oocytes were warmed and inseminated with ICSI. Embryological parameters were recorded and compared between fresh and sibling vitrified oocytes (intrapatient) as well as between the two vitrification techniques (interpatient). Oocytes vitrified with the 'closed' system showed significantly lower fertilization and cleavage rates and a reduction in the quantity and quality of obtained embryos compared with fresh sibling oocytes (P<0.001). On the contrary, the same parameters were similar between fresh and sibling oocytes vitrified using the 'open' system. The retrospective comparison between the two vitrification protocols also showed a significant increase in clinical pregnancy rate and a reduced proportion of cancelled cycles using the 'open' system (P<0.01).