Embryo retention and live birth in frozen embryo transfer cycles: a cohort study

To study the effect of embryo retention in the transfer catheter on pregnancy outcomes in frozen embryo transfer (FET) cycles.

Retrospective cohort study.

This retrospective study involved a total of 39,118 women who underwent FET cycles at a tertiary-care academic medical from January 2016 to December 2022.

Women were divided into a control group (n = 38,933) and embryo retention group (n = 185). The women in the embryo retention group had been propensity scores matched with those in the control group at a 1:4 ratio.

The primary outcome was live birth (LB). The secondary outcomes were biochemical pregnancy, clinical pregnancy (CP), miscarriage, and ectopic pregnancy.

The overall incidence of embryo retention in the transfer catheter was 0.47% (185/39,118). The pregnancy outcome in the embryo retention group after propensity score matching (PSM) was comparable to that before PSM, with a reduced likelihood of biochemical pregnancy (odds ratio [OR], 0.83; 95% confidence interval [CI], 0.72-0.95), CP (OR, 0.81; 95% CI, 0.69-0.96), and LB (OR, 0.80; 95% CI, 0.66-0.97). In addition, the birth weight in the embryo retention group was higher compared with the control group. However, no differences were observed in terms of miscarriage, ectopic pregnancy, cesarean delivery, as well as gestational age both before and after PSM.

Embryo retention in the transfer catheter decreases the chance of biochemical pregnancy, CP, and LB in FET cycles.