Assessing the risk of ectopic pregnancy following euploid frozen embryo transfer: a retrospective cohort study

To evaluate possible risk factors for an ectopic pregnancy after euploid frozen embryo transfer (FET) at blastocyst stage.

Retrospective cohort study of women with a positive pregnancy test after euploid frozen embryo transfer at blastocyst stage between April 2017 and June 2023.

An ectopic pregnancy occurred in 21 patients (1.19%) out of 1758 patients. Patient characteristics age, BMI, smoking status, infertility type, cycle/embryo characteristics (type of endometrial preparation and embryo quality), and presence of an isthmocele (yes/no) were not significantly different between the patients with versus without an ectopic pregnancy. The ratio measured to expected hCG levels was significantly lower in patients with ectopic pregnancy when compared to those with clinical pregnancy (0.7 vs 1, P < 0.001). The multinomial regression analysis showed increased odds of an ectopic pregnancy (EP) compared to an ongoing clinical pregnancy with lower observed/expected hCG levels in both single and double embryo transfers (OR, 0.4; 95% CI, 0.07-0.25; P < 0.001 and OR, 0.16; 95% CI, 0.09-0.30; P < 0.001).

The risk of ectopic pregnancy in euploid frozen embryo transfer cycles at the blastocyst stage is comparable to spontaneous conceptions. Despite the huge sample size of euploid FET cycles, due to the very low number of ectopic pregnancies, we were unable to identify a particular risk factor for ectopic implantation.