Fig. 1

Endometrial patterns based on the Gonen system. Type A: trilaminar pattern (endometrial three-layer pattern) consisting of hyperechoic outer and middle layers, hypoechoic inner layers, and evident echo at the intrauterine midline; type B: relatively homogeneous hyperechoic endometrium, with unclear endometrial layers, obscure intrauterine midline echo, but clear interface between endometrial and muscular layers; type C: homogeneous hyperechoic endometrium without intrauterine midline echo