Effect of endometrial thickness on ectopic pregnancy in frozen embryo transfer cycles: an analysis including 17,244 pregnancy cycles

Endometrial thickness is inversely proportional to ectopic pregnancy (EP) rate in frozen embryo transfer (FET) cycles, and hormone replacement treatment for endometrial preparation during FET increases EP risk.

Volume 113, Issue 1, Pages 131–139


Hongfang Liu, M.D., Jie Zhang, M.D., Bian Wang, M.D., Yanping Kuang, M.D.



To investigate whether endometrial thickness (EMT) influences the incidence of ectopic pregnancy (EP) in frozen embryo transfer (FET) cycles.


Retrospective cohort study.


Academic tertiary-care medical center.


A total of 16,556 patients were enrolled between January 2010 and December 2017, comprising 16,701 intrauterine, 488 ectopic, and 45 heterotopic pregnancy cycles after FET.



Main Outcome Measure(s)

EP was the primary outcome. EMT was the main measured variable. Data were analyzed with the binary logistic general estimating equations model to calculate the adjusted odds ratio (aOR) for EP.


After adjusting for confounders, EMT remained statistically significant as an independent risk factor for EP. Compared with women with an EMT of ≥14 mm, the aORs for women with EMT in the ranges 7–7.9, 8–9.9, and 10–11.9 mm were 2.70 (95% confidence interval [CI], 1.65–4.40), 2.06 (95% CI, 1.33–3.20), and 1.66 (95% CI, 1.07–2.58), respectively. Hormone replacement treatment for endometrial preparation during FET increased the risk of EP after adjustment for confounding variables.


EMT is inversely proportional to EP rate in FET cycles and is therefore a potential quantitative marker of endometrial receptivity and uterine contractibility in an FET cycle. The predictive validity of EMT value must be evaluated in further studies.

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