The prolonged storage time of vitrified embryos negatively affects pregnancy outcomes, including biochemical pregnancy rate, clinical pregnancy and live birth rate, but does not influence neonatal outcomes. That is the finding of a retrospective study published in the journal Human Reproduction.
The study was carried out among 24,698 patients with first vitrified embryo transfer following a freeze-all strategy, during the period from January 2011 to December 2017. Participants were grouped according to storage time
- Group 1: storage time
- Group 2: storage time 3-6 months (n=9614)
- Group 3: storage time 6-12 months (n=3188)
- Group 4: storage time 12-24 months (n=566)
Compared to Group 1, the chance of biochemical pregnancy, clinical pregnancy and live birth significantly decreased with increasing storage time.
The relationship between miscarriage, ectopic pregnancy and storage time did not reach statistical significance, and there was no evidence of differences in adverse neonatal outcomes.
The authors say the findings offer evidence for the safety of using long-stored embryos after vitrification.
The study was limited by the retrospective design from a single centre, and the conclusions will need to be verified in further studies.