O-293: Vitrified oocytes produce excellent pregnancy rate

Abstract

Successful cryopreservation of human oocytes is the crucial element in treating women who desire future pregnancies. With continuous improvements in knowledge and technique of cryobiology, success rates of frozen embryo pregnancy have risen over the last two decades to the point that now the embryo cryopreservation has become a routine part of modern ART practices. However, advances in oocyte cryopreservation technology are still stagnant and controversial despite intense public interest. Although the progress is intermittent and frustrating at times, more centers around the world are reporting improved techniques and successful outcomes (pregnancies) for the last few years. One of the promising areas of research is a flash freezing method or vitrification. The objective of this study is to demonstrate the ability to successfully cryopreserve human oocytes using vitrification method. Development of a new approach to improve the clinical efficiency (pregnancy) of vitrified oocytes. Oocytes vitrification was performed in two steps process. Oocytes were first equilibrated in cryoprotectant solution containing 1.5M ethylene glycol at 37°C for 2.5 min followed by treatment with vitrification solution containing 5.5M ethylene glycol and 1M sucrose for 20 second at room temperature. Oocytes were then placed on the electron microscope (EM) grids, and immediately plunged into the liquid nitrogen. A total of 1,499 oocytes from 63 patients (70 procedures) were cryopreserved using vitrification technique. Thawing was 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 2.5min intervals at 37°C. The oocytes were fertilized by ICSI and fertilized embryos were transferred to the uterus 3days, 5days or 6days after thawing. From 63 patients, a total of 70 egg retrieval procedures were performed for oocytes cryopreservation. Of those, 26 patients came back to utilize their 464 vitrified oocytes. 376 out of 464 oocytes survived after thawing (81%). Fertilization rate and cleavage rate were 63.8% (220/345) and 95.9% (211/220) respectively. Average number of transferred embryos was 3.2 ± 1.1. Nineteen of twenty six patients (73.1%) became pregnant, and implantation rate based on ultrasound exam was 33.7% (28/83). Ten patients delivered seventeen healthy babies (three set of triplet and one set of twin). One of patients who delivered triplets had undergone selective reduction procedure at the end of the 1st trimester to reduce from five gestational sacs down to three. Five patients encountered miscarriages (five sacs) around 6 weeks of gestation. Four patients are currently on going in their 1st and 2nd trimesters. Our data shows high efficacy of vitrification method in maintaining oocyte viability. Higher than expected miscarriage rate is somewhat concerning. It appears that oocytes that survive freezing may have lost some developmental potential. To prevent multiple pregnancy outcome, we started blastcyst transfers in almost all cases to reduce the number embryos transferred. More data from our ongoing study will be available in a year to further elucidate the efficacy of this method and better statistical analysis. It is our goal to continuously improve and optimize this technology so that this would eventually become a part of treatment options in future ART practices.