Does longer storage of blastocysts with equal grades in a cryopreserved state affect the perinatal outcomes?

Although mammalian embryos could be preserved in liquid nitrogen for thousands of years in theoretical models, the viability of cryopreserved blastocyst with varying grades remains to be speculated. In this study, we aimed to determine whether the longer storage time of blastocysts with equal grades could negatively affect the perinatal outcomes. Single vitrified-warmed blastocyst was divided into four grades (AA, AB/BA, BB, BC/CB) according to the blastocyst score when freezing, and each grade of blastocyst was categorized into four storage duration categories: 28 days-1 year, 1–3 years, 3–5 years, and ≥5 years. Then the perinatal outcomes with different storage time were analyzed. Our results revealed that for blastocysts with the same grade, the length of storage time had no statistical effect on blastocyst survival rate, clinical pregnancy/implantation rate, live birth rate, and abortion rate. In addition, more advanced developmental blastocyst could obtain better pregnancy outcomes regardless of the cryopreservation length. Similar neonatal outcomes were obtained over time. Cryopreservation time could not negatively affect the perinatal outcomes of blastocysts with equal grades. Efficient blastocyst cryopreservation technology by vitrification can help older women obtain high-quality embryos at a young age.