Impact of embryo storage time after vitrification on pregnancy and implantation rates.

Objective: The study aimed to assess whether the storage time after vitrification affects clinical pregnancy and implantation rates.

Methods: This multicentric retrospective study involved 1568 cycles of autologous frozen embryo transfers between 2015 and 2019. The patients were divided into groups based on storage time to assess its impact on pregnancy and implantation rates. The variables analyzed were maternal age, cryopreservation stage, and embryo transfer" stage. Logistic regression was used to investigate associations between storage duration, patient age, and transfer outcomes. The study was approved by the Research Ethics Committee of UFMG and informed written consent was waivered.

Results: The length of embryo storage showed an inverse association with pregnancy and implantation rates, correlating with patient age and embryo stage at the time of transfer. Patients aged 36 to 40, and 41 years or older had lower rates of clinical pregnancy compared to those under 35 years of age. Additionally, vitrified embryos transferred at the cleavage stage demonstrated lower rates of clinical pregnancy and implantation compared to those at the blastocyst stage. These results suggest that storage duration, patient age, and embryo stage significantly influence frozen embryo transfer (FET) outcomes.

Conclusions: Storage duration, patient age, and embryo stage can affect FET outcomes, with older women and embryos at the cleavage stage, possibly experiencing lower pregnancy and implantation rates after extended storage.