Storage time does not influence pregnancy and neonatal outcomes for first single vitrified high-quality blastocyst transfer cycle.

ABSTRACT

RESEARCH QUESTION Does blastocyst storage time have an impact on pregnancy and neonatal outcomes following the first single vitrified/warmed high-quality blastocyst transfer cycle for young women? DESIGN: Retrospective cohort study in a university-affiliated reproductive medical centre. RESULTS: A total of 2938 patients undergoing their first frozen embryo transfer (FET) cycle with a single high-quality blastocyst (Day 5 3BB and above; Day 6 4BB and above) transferred were divided into five groups Group A with storage time ≤3 months (n = 1621), Group B with storage time of 4-6 months (n = 657), Group C with storage time of 7-12 months (n = 225), Group D with storage time of 13-24 months (n = 104), and Group E with storage time of 25-98 months (n = 331). After adjusting for confounding factors by multivariate logistic regression, there were no significant differences in live birth rate [Group A as reference; Group B adjusted odds ratio (aOR) 0.954 (95% CI 0.791- 1.151); Group C aOR 0.905 (95% CI 0.674-1.214); Group D aOR 0.727 (95% CI 0.474-1.114); Group E aOR 1.185 (955 CI 0.873-1.608)], ß-human-chorionic-gonadotropin-positive rate, clinical pregnancy rate and miscarriage rate between Group A and the other groups. Among all singletons born after FET, there were no significant differences with regards to gestational age, preterm birth, birthweight, low birthweight, high birthweight and macrosomia. CONCLUSION: Long-term cryostorage of human vitrified high-quality blastocysts does not affect pregnancy or neonatal outcomes.