Whether endometrial lining of 0.3cm is normal or not needs to be decided according to the specific menstrual cycle because the thickness of endometrial lining changes with the cyclical changes of hormones secreted by the ovaries. The thickness of the endometrium is not a fixed value, usually when the menstrual period is just clean, due to the low level of estrogen in the body, the endometrium is thinner at this time, the thickness of the endometrium is mostly 0.3-0.5cm. if the endometrium thickness is 0.3cm at this time, it is mostly normal. If the endometrial thickness is 0.3cm during ovulation, it is usually abnormal. During ovulation, due to the increase of estrogen level in the body, the thickness of the endometrium is usually around 0.8cm, which is helpful for pregnancy, and the thickness of the endometrium usually reaches 1.0-1.5cm before menstruation.