Effect of embryo retention on in vitro fertilization outcomes: a retrospective analysis

To evaluate the incidence of embryo retention (ER) during blastocyst single embryo transfer (SET) cycles and assess its impact on reproductive outcomes in vitro fertilization IVF.

In this retrospective cohort study, 4593 SET cycles from 3061 patients treated at a single IVF center between October 2021 and July 2024 were analyzed. Cycles were categorized according to the occurrence of ER during embryo transfer (ER group, n = 106; control group, n = 4487). Both fresh and frozen transfers using autologous or donor oocytes were included. The primary outcome was live birth rate (LBR). Secondary outcomes included implantation, biochemical pregnancy, clinical pregnancy, ongoing pregnancy, and miscarriage rates. Logistic regression analyses were performed to evaluate associations between ER and reproductive outcomes.

ER occurred in 2.3% of SET cycles. Implantation and early pregnancy outcomes were significantly lower in the ER group compared with controls. After adjustment, ER remained significantly associated with lower implantation (aOR 0.84, 95% CI 0.76-0.92; p < 0.001), biochemical pregnancy (aOR 0.49, 95% CI 0.32-0.75; p < 0.001), and clinical pregnancy rates (aOR 0.53, 95% CI 0.34-0.82; p = 0.004). No statistically significant associations were observed for ongoing pregnancy, live birth, or miscarriage.

In this cohort, ER during single blastocyst transfer was associated with lower implantation and early pregnancy rates. These findings should nevertheless be interpreted in light of the potential influence of procedural factors associated with embryo transfer. The association between ER and ongoing pregnancy or live birth remains inconclusive.