Embryo survival after vitrification of 2 PN oocytes

ObjectiveTo assess embryo survival after vitrification of 2 PN oocytes and evaluate the impact of the duration of cold storage and patient age.SettingDepartment of Obstetrics and Gynaecology, Division of Reproductive Endocrinology and Infertility, Schleswig-Holstein University, Campus Luebeck.DesignRetrospective study.Materials and methodsCohort analysis of 576 thawing cycles after vitrification performed between 2004 and 2010. Results were used to construct a model to predict the embryo survival based on vitrification cycles. Data were categorized with respect to the duration of cold storage, number of 2 PN oocytes on each cryo-top, and patient age.Main outcome measuresThe survival rate of 2 PN zygotes after thawing, implantation rate (IR) per transferred embryo, and clinical pregnancy rate (CPR).ResultsIn 576 thawed cycles, the survival rate of 1.349 2 PN warmed zygotes was 89.39%. Similar results concerning the survival rates of the 2 PN oocytes after thawing for all age groups (<30 years, 85.67%; 30–34 years, 89.21%; 35–40 years, 91.8%; >40 years, 99.9%) were noted. A total of 1159 embryos were transferred, leading to an overall IR of 7.72% and a CPR of 16.3%. The CPR decreased with age, as follows: CPR <30 years, 28.6%; 30–34 years, 16.5%; 35–40 years, 9.2%; >40 years, 5.8%. No significant association between the duration of cold storage and the number of 2 PN oocytes on each carrier on the embryo survival rate in question was observed.ConclusionThe duration of cold storage has no significant influence on the PR. Undoubtedly, age is a limiting factor in assisted reproduction as can be seen through a decreasing PR with increasing age.