Impact of prolonged embryo storage on reproductive and neonatal outcomes: a systematic review and meta-analysis

To analyze the influence of embryo storage on reproductive and neonatal results in patients undergoing in vitro fertilization (IVF) treatment.

PubMed, Embase, Cochrane Central Register of Controlled Trials, and BioMed Central databases were searched from inception up to June 2024 for studies comparing reproductive and neonatal outcomes in patients undergoing frozen embryo transfer within 12 months from embryo storage versus more than 12 months after embryo storage. Data were pooled by meta-analysis using a random effects model.

A total of 16 studies, involving 233,315 embryos were included. Patients undergoing frozen embryo within 12 months from embryo storage were associated with higher rates of live birth (OR 1.17, 95% CI 1.09-1.26, I² = 78%) biochemical pregnancy (OR 1.26, 95% CI 1.08-1.47, I² = 77.8%) clinical pregnancy (OR 1.24, 95% CI 1.12-1.38, I² = 86.3%) and multiple pregnancy rate (OR 1.26, 95% CI 1.03-1.55, I² = 69%). No significant differences between groups were shown in terms of survival rate (OR 1.52, 95% CI 0.65-3.58, I² = 98.5%), miscarriage (OR 1.08, 95% CI 0.91-1.27, I² = 77%), implantation rate (OR 1.17, 95% CI 0.90-1.52, I² = 91.7%) and ectopic pregnancy (OR 0.98, 95% CI 0.80-1.20, I² = 0%). In addition, prolonged embryo storage was not associated with higher rates of preterm delivery (OR 0.86, 95% CI 0.67-1.09, I² = 8.3%), low weight at birth (OR 1.10, 95% CI 0.88-1.38, I² = 24.3%) or congenital malformations (OR 0.90, 95% CI 0.65-1.25, I² = 0.8%).

Prolonged embryo storage over 12 months is associated with lower rates of live birth, biochemical pregnancy, clinical pregnancy, and multiple pregnancy. However, important covariates such as reasons for delay of transfer, embryo quality, and improper handling of embryos could not be ruled out as causes of this reduction. Given these limitations, these conclusions should be viewed with caution.