Embryo retention significantly decreases clinical pregnancy rate and live birth rate: a matched retrospective cohort study.

Objective: To investigate the embryo retention (ER) rate in embryo transfer (ET) cycles and its effects on reproductive outcomes.

Design: Matched retrospective cohort study.

Setting: A tertiary hospital-based reproductive medicine center.

Patient(s): A total of 6,089 ET cycles were performed from January 2013 to December 2018 in our unit.

Intervention(s): Each woman was matched with two separate control subjects of the same age (±1 year), embryo condition, main causes of infertility, type of protocol used for fresh or frozen ET cycles.

Main Outcome Measure(s): ER rate, implantation, clinical pregnancy, ectopic pregnancy, and live birth rate.

Results: The overall incidence of ER was 1.59% (97/6,089). A significantly increased ER rate was observed in fresh ET cycles compared with frozen transfer cycles (2.71% vs. 1.08%). In fresh transfer cycles, the rate of mucus in or on the catheter after ET in ER group was significantly higher than in the non-ER group (48.09% vs. 13.65%). A total of 194 non-ER cycles were matched to the ER group. Compared with the matched group, the ER group was associated with a significantly lower clinical pregnancy rate (32.98% vs. 48.96%), implantation rate (20.88% vs. 35.97%), and live birth rate (22.68% vs. 37.63%, P<.01), and a higher ectopic pregnancy rate (12.50% vs. 3.16%).

Conclusion: Our results suggest that ER rate is correlated with mucus on or in the transfer catheter in fresh transfer cycles. Retained embryos are associated with lower implantation, clinical pregnancy, live birth, and increases risk of ectopic pregnancy.