Impact of endometrial thickness during menstruation and endometrial scratching on the pregnancy in frozen–thawed embryo transfer

AIM: This study aimed to investigate the impact of endometrial thickness (EMT) during menstruation and endometrial scratching on the pregnancy in frozen-thawed embryo transfer (FET). METHODS: About 1298 patients receiving FET were retrospectively analyzed and divided according to EMT on the 4th or 5th day of menstruation. Group A: EMT ≤ 3.0 mm; Group B: EMT 3.1-5.0 mm; Group C: EMT 5.1-7.0 mm and Group D: EMT > 7.0 mm. Patients in Group D were further divided to scratching group and nonscratching group. Endometrial growth was defined as the change in EMT from 4th or 5th day of menstruation to the day of embryo transferred. RESULTS: We found no significant differences in general conditions among four groups (P > 0.05). The average EMT during menstruation and differences in inter-group endometrial growth of four groups had statistical significance (P < 0.05). The pregnancy rate and implantation rate of Group D were significantly lower than other groups (P < 0.001). Pregnancy rate (68.29% vs 53.26%) and implantation rate (52.67% vs 36.34%) in endometrial scratching group were higher than those in nonscratching group (P < 0.05). CONCLUSION: Higher EMT during menstruation adversely affects pregnancy outcomes following FET. Endometrial scratching may improve the receptivity of endometrium and increase the rate of embryo implantation and pregnancy.