A 0.4 cm endometrium without a period is caused by a relatively thin endometrium. The endometrium has different thicknesses at different times of the menstrual cycle. Before menstruation, the endometrium will be relatively thick, usually between 10 and 12 millimeters. If there is no menstruation for a long time, but the endometrium is only 0.4 centimeters in ultrasound examination, this situation is abnormal and may be caused by endocrine disorders. For example, women with hyperprolactinemia will have relatively low levels of estrogen, which is not conducive to the repair of the uterine lining, leading to a thin endometrium, resulting in scanty menstruation or amenorrhea. For this kind of endometrial thinning, you can take short-acting contraceptive pills under the guidance of the doctor for a period of time, such as taking drospirenone ethinyl estradiol tablets, or deoxypregnene ethinyl estradiol tablets and so on. You can also take Chinese medicines, such as regulating menstruation and promoting pregnancy pills, Kuntai capsule and so on. Then come to menstruation 2 ~ 4 days, blood test sex hormone 6, and then targeted selection of drugs to regulate.