Does endometrial thickness affect ectopic pregnancy risk after frozen embryo transfer?

This study investigated the effect of endometrial thickness (EMT) on ectopic pregnancy (EP) risk after frozen embryo transfer (FET). 

They found that lower a EMT was associated with a higher risk of EP after FET.

Ectopic pregnancy (EP) is caused by a pregnancy growing outside the uterus. EPs are not viable pregnancies. They can also lead to a loss of fertility if women are not treated in time. It can also be life-threatening. EPs are more common after assisted reproduction (AR) than natural conception. The reason for this is unclear. 

Endometrial thickness (EMT) is an important factor during embryo transfer. EMT refers to the thickness of the uterus lining. The optimal EMT  to get pregnant is more than 14 mm. Reduced EMT is associated with poorer pregnancy outcomes after fresh (FrET) or frozen embryo transfer (FzET). This is because the endometrium (uterus lining) supports the growing embryo. The relationship between EMT and EP in women undergoing FzET is unclear. 

This study included 16,556 women undergoing FzET. 488 women had an EP. Patient data and POs were obtained from medical records. All patients underwent AR procedures in the same hospital. Endometrial preparation was performed using different methods. EMT was measured before embryo transfer. 

When compared to women with an EMT of 14 and higher, an EMT of 7- 7.9 mm was associated with a 2.7-fold increase in EP. The risk of EP was 2-fold greater with an EMT of 8- 9.9 mm. Lower EMT was associated with a higher risk of EP after FzET.

EMT induced using mild stimulation was associated with a 47% risk of EP. Hormone replacement therapy stimulation for EMT was associated with a 2.25 times higher risk for EP.  The embryo stage at embryo transfer was also associated with EP. Cleavage-stage embryos had a 2.87-fold higher risk of EP. 

The authors concluded that lower EMT was associated with a higher risk of EP after FzET.

This study was based on data from medical records. Some factors may not be accounted for. Smoking is known to increase EP risk. This was not considered in this study. 

If you have any concerns regarding infertility please consult with your doctor.