Objective: To evaluate whether prolonged storage of vitrified blastocysts negatively impacts pregnancy and neonatal outcomes.
Design: A retrospective cohort study.
Setting: University hospital.
Patient(s): A total of 6,900 patients who desired to transfer vitrified blastocysts from the same oocyte retrieval cycle as their last live birth met the inclusion criteria and were grouped according to the storage duration (1,890 patients in group 1 with storage duration < 3 years, 2,693 patients in group 2 with storage duration between 3 and 4 years, 1,344 patients in group 3 with storage duration between 4 and 5 years, 578 patients in group 4 with storage duration between 5 and 6 years and 395 patients in group 5 with storage duration ≥ 6 years but ≤ 10.5 years).
Intervention(s): None.
Main outcome measure(s): Rates of blastocyst survival, biochemical pregnancy, clinical pregnancy, miscarriage, ectopic pregnancy, and live birth and neonatal outcomes.
Result(s): The survival rates of the vitrified blastocysts significantly decreased with prolonged storage from group 1 to the subsequent groups 2, 3, 4, and 5. After adjusting for potential confounding factors, the rates of biochemical pregnancy, clinical pregnancy, and live birth were significantly decreased when the vitrified blastocysts were stored for more than 6 years (group 5) compared with these for less than 3 years (group 1) but no distinct differences were found in these above-mentioned indicators among group 1, 2, 3, and group 4 (group 1 as reference). However, no significant differences were noted in the rates of miscarriage and ectopic pregnancy and neonatal outcomes on prolonged storage of vitrified blastocysts.
Conclusion(s): Long-term blastocyst vitrification for more than 6 years can negatively affect the rates of biochemical pregnancy, clinical pregnancy, and live birth but does not impact neonatal outcomes.
Keywords: Storage duration; blastocysts; neonatal outcomes; pregnancy outcomes; vitrification.
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