The endometrial thickness of 0.4cm is normal and needs to be judged according to the examination time. The thickness of the endometrium changes at different times: 1, If the endometrial thickness of 0.4cm is detected during ovulation, it is not normal and may be due to various conditions such as a thin endometrium. Under normal circumstances, the thickness of the endometrium during ovulation is about 8-13mm, if too thin, too thick are abnormal, may be a disease response, it is best to timely symptomatic treatment, so as not to have an impact on the body.