To explore the influence of different endometrial thickness (EMT) during menstrual period on pregnancy outcomes in frozen-thawed embryo transfer (FET), and to evaluate the effect of endometrial scratching in patients whose EMT were more than 7 mm.

The data of 1 363 patients accepting FET were retrospectively analyzed. The patients were divided into five groups according to their EMT on the 4th or 5th day of menstruation. Group A: EMT < 3 mm; group B: EMT 3-5 mm; group C: EMT 5-7 mm; group D: EMT > 7 mm; group E: fluid within the endometrial cavity. Patients in group D were further divided into scratching group and non-scraping group. The general conditions, clinical pregnancy rate, implantation rate and ectopic pregnancy rate of patients were compared.

There were no significant differences in general conditions among the five groups (P>0.05). The average EMT during menstruation and differences in inter-group endometrial growth of the five groups had statistical significances (P<0.05). The average endometrial growth of EMT < 7 mm (group A, group B and group C) was significantly higher than that in group D (P<0.005). The pregnancy rate and implantation rate of group D were significantly lower than those in other groups (P<0.005). While the clinical pregnancy rate and implantation rate in endometrial scratching group (68.29%, 52.67%, respectively) were higher than those in non-scraping group (53.26%, 36.34%, respectively) (P<0.05).

EMT during menstruation >7 mm can adversely influence pregnancy outcomes in FET. Endometrial scratching may improve the receptivity of endometrium and increase the rate of embryo implantation and pregnancy.

Frozen-thawed embryo transfer (FET); Endometrial thickness during menstruation; Endometrial growth; Endometrial scratching; Pregnancy outcomes