Oocyte Cryopreservation Comparing Fresh and Vitrified Sibling Oocytes

Overview

Vitrification is a method to cryopreserve biological specimens that are sensitive to chilling injury such as oocytes and embryos, and it has been employed with increased survival rate and live births (Hong et al., 1999; Kuleshova et al., 1999; Yoon et al., 2000; Chung et al 2000; Wu et al., 2001: Kuwayama et al 2006). In their study the researchers propose to directly compare oocyte survival, fertilizaton and embryo development between sibling oocytes. The Cryotop method of vitrification, which the researchers aim to investigate in their study, has been reported as the most efficient method for human oocytes cryopreservation (Kuwayama et al, 2005, Antinori et al, 2006, Lucena et al, 2006, Cobo et al, 2008). Follow up of over 200 infants conceived from vitrified oocytes (Chian et al, 2008) indicate that the mean birth weight and the incidence of congenital anomalies are comparable to that of spontaneous conceptions in fertile women or infertile women undergoing IVF treatment.

The necessity to cryopreserve human oocytes successfully, with the goal of achieving term pregnancies at rates equivalent to those obtained with fresh oocytes is urgent. Cryopreservation of oocytes is desirable because: 1) it would allow infertility patients to store excess oocytes instead of embryos, eliminating some of the ethical and religious concerns that accompany embryo storage; 2) permit storage of donor oocytes in egg banks, analogous to existing sperm banks. This option would allow the cryopreserved oocytes to be quarantined until screening for infectious diseases is completed, and would also avoid donor-recipient synchronization difficulties; and 3) can help cancer patients preserve their fertility before they face sterilization due to chemotherapy or radiation. Oocyte cryopreservation is therefore gaining in popularity as an option for infertility treatment as well as fertility preservation. This is a pilot study to evaluate the outcomes of oocyte vitrification using the Cryotop method in women undergoing IVF, by simultaneously evaluating embryos derived from vitrified and fresh oocytes coming from the same stimulated cycle. The primary outcome measures that will be tracked and tabulated are oocyte survival, fertilization and cleavage rate, and subsequent embryo development, compared between vitrified and fresh oocytes. Secondary outcomes are implantation, clinical pregnancy, miscarriage and live birth rates using embryos derived from the vitrified oocytes for transfer.