Ectopic pregnancy after in vitro fertilization: differences between fresh and frozen-thawed cycles

Objective: To evaluate whether the uterine environment is associated with the risk of ectopic implantation by comparing outcomes of fresh and frozen-thawed embryo transfers.

Design: Retrospective historical cohort.

Setting: Not applicable.

Patient(s): We used the Society for Assisted Reproductive Technologies (SART) database to identify pregnancies that resulted from fresh and frozen blastocyst transfers from 2008 to 2011.

Intervention(s): None.

Main outcome measure(s): We determined the proportion of ectopic (EP) versus intrauterine-only pregnancies resulting from fresh or frozen embryo transfers in autologous and donor-oocyte cycles. Generalized estimation equation regression models were used to adjust for maternal and treatment characteristics.

Result(s): Among 103,070 cycles that resulted in a clinical pregnancy, 1.38% were ectopic. The odds of EP were 65% lower in women who had a frozen compared with a fresh transfer in autologous cycles. Donor-oocyte transfers had lower odds of EP compared with autologous cycles, with no difference between fresh and frozen donor transfers. Women who had both a fresh and a frozen transfer with autologous oocytes had a higher risk of EP in their fresh cycles compared with their frozen cycles.

Conclusion(s): Embryo transfers in cycles without ovarian hyperstimulation, such as frozen or donor cycles, were associated with lower rates of EP compared with fresh autologous cycles, suggesting that a difference in the tubal-uterine environment contributes to abnormal implantation after IVF.