Structural and reproductive implications of oocyte vitrification and thawing

Abstract

Vitrification is a fundamental tool in assisted reproduction that allows the cryopreservation of embryos and gametes avoi- ding the formation of ice. Oocyte vitrification has been a great technological advance not only for treating patients with fertility problems, but also as a means for women to cryopreserve their oocytes and, therefore, increase the chances of conceiving in the future. The remarkable clinical results in cycles with vitrified oocytes have boosted the development and use of donation programs, especially since the second half of the last decade, and have made oocyte vitrification a basic and widely used technique in routine clinical practice. However, scientists expert in reproductive biology and tech- nology have published that vitrification can have consequences on the oocyte itself. In fact, it has been shown to affect: ultrastructure, zona pellucida, calcium levels, meiotic spindle and oocyte gene expression, as well as several parameters related to mitochondria appear to be altered. In this sense, it would be necessary to compare the competence and efficiency of oocytes that have been vitrified versus those that have been used fresh and, consequently, have not undergone this pro- cedure. After analyzing several articles comparing the use of both types of oocytes and reflecting the results in embryo- logical and obstetric terms such as survival rates, fertilization, division, embryo quality at different days of development, implantation rates, pregnancy in progress and live newborn, among others, it is possible to affirm that, in general terms, they are comparable between both groups. Likewise, some studies have shown that there is no greater incidence of perinatal alterations with the use of oocytes previously submitted to vitrification as opposed to fresh ones.