A novel method for human oocyte vitrification with a closed device using super-cooled air

Abstract

Human oocytes have been successfully vitrified with open systems that involve direct contact with liquid nitrogen. Concerns have been raised regarding the safety and sterility of this methodology. It is therefore highly desirable to use a device that does not utilize direct contact with liquid nitrogen during vitrification and storage. It is thought, however, that the high cooling rate afforded by direct liquid nitrogen contact is essential for human oocyte vitrification. Human oocytes were collected from donors and vitrified/warmed for transfer into recipients. Following oocyte warming; fertilization, embryo development, implantation, biochemical pregnancy and clinical pregnancy rates were recorded. The results were compared retrospectively to data from non-vitrified oocytes within the same time period. Almost 600 oocytes from 53 donors were vitrified using a newly developed vitrification medium specifically for oocytes (RapidVit and RapidWarm Oocyte: Vitrolife AB) and a closed vitrification device that uses a straw with super-cooled air (Rapid-i™: Vitrolife AB). Oocytes were collected from 53 oocyte donors (mean age of 24.6 ± 4.0) and vitrified/warmed. The survival and fertilization rates were 94 % and 76 %, respectively. A mean number of 1.8 ± 0.5 embryos were transferred on day 5/6 per recipient (mean age 40.4 ± 4.6). The implantation rate was 34.4 % (33/96). The biochemical and clinical pregnancy rates were 65 % (33/51) and 51 % (26/51), respectively. The ongoing (>12 weeks) pregnancy rate was 49 % with 5 healthy live births reported so far. These results were not statistically different from outcomes with non-vitrified oocytes. This study demonstrates that, despite lower cooling rates, human oocytes can be vitrified without direct contact with liquid nitrogen in a closed device (Rapid-i™). A closed system that uses super-cooled air to vitrify removes the potential concerns regarding contamination from liquid nitrogen.