Title: Pregnancy and Delivery After Vitrification of Human Oocytes
Abstract: Objective: As the cryopreservation technique improves, effective freezing method of human oocytes has generated intense interest and controversies. Despite intermittent success by several centers around the world, oocyte cryopreservation still remains an illusive task for the reproductive medicine scientists. One of the promising areas of research is a flash freezing method or vitrification. Many publications have documented impressive pregnancy rates with vitrification of embryos. The objective of this study is to demonstrate the ability to successfully freeze human oocytes using vitrification method. Design: Development of a new approach to improve the clinical efficiency (pregnancy) of vitrified oocytes. Materials and Methods: Oocytes vitrification was performed in two steps as following. Oocytes were first equilibrated in cryoprotectant solution containing 10% ethylene glycol at 37°C for 5 min followed by introducing vitrification solution containing 38% ethylene glycol and 1M sucrose for 20 second. Oocytes were then placed on the EM grid and immediately plunged to the liquid nitrogen. A total of 862 oocytes from 40 patients (46 procedures) were cryopreserved using vitrification technique. Thawing is performed according to five step protocol using 1.0M, 0.5M, 0.25M, 0.125M, 0M of sucrose solutions. The EM grids were transferred sequentially to the thawing solutions at intervals of 2.5min. The oocytes were fertilized by ICSI and fertilized embryos were transferred to the uterus 3days after thawing. Results: For 40 patients, a total of 46 procedure of oocytes cryopreservation were performed and 186 of vitrified oocytes from ten patients were thawed. Survival rate was 74.7% (139/186). Fertilization rate and cleavage rate were 55.2% (58/105) and 87.9% (51/58) respectively. Four of ten patients became pregnant with implantation rate of 15.3% (6/39). Two patients miscarried at 7 weeks of gestation. Two pregnant patients delivered 4 babies, one set of triplet and one of singleton. Conclusion: This study shows limited efficacy of vitrification method in maintaining oocyte viability. However, it appears that oocytes that survive freezing may have lost some developmental potentials. Preimplantation genetics diagnosis may help improve the implantation rates for these embryos. More data should be available in a year to evaluate the efficacy of this method with more statistical power. It is our goal to continuously improve and optimize this technology so that this could eventually become a routine application in future ART practice.