An endometrial lining of 0.9 cm often indicates the imminent onset of menstruation. If you haven’t had your period yet, you usually need to be patient for another week or two, and often you will have your period within a week or two. If you wait a week or two and still do not get your period, you should look for the cause and take care of it. Generally speaking, when a woman’s menstrual cycle is about 4 weeks old, the endometrium gradually thickens. Before menstruation, the ovarian corpus luteum atrophies on its own, estrogen and progesterone drop, and the endometrium peels off, leading to the onset of menstruation. At this time, the endometrial lining is usually about 1cm thick, but of course, sometimes the endometrial lining is close to 2cm thick before menstruation occurs. An endometrial thickness of 0.9cm is already relatively thick and may indicate the onset of menstruation. However, if you wait for a week or two and still have a period, it is usually necessary to check blood and urine HCG to exclude the possibility of pregnancy and further exclude special cases such as ectopic pregnancy and embryonic abortion if necessary. After ruling out pregnancy, occasional delayed menstruation is often associated with female mental and psychological factors, such as exam tension, work stress and bad mood, which sometimes interfere with hypothalamic-pituitary-ovarian function and lead to delayed menstruation. For endometrium 0.9cm, if there is a delay in menstruation, progestogenic drugs can be given to promote the onset of menstruation, such as diprogesterone, progesterone capsules, etc. There is often a menstrual flow during the medication or within 2 weeks after stopping the medication. If there is frequent delay in menstruation, female sex hormone test and thyroid function should be checked to rule out endocrine diseases such as polycystic ovary syndrome, hyperprolactinemia, abnormal thyroid function and premature ovarian failure. If the test is related to hyperprolactinemia, which usually manifests as elevated blood prolactin and delayed menstruation or no menstruation, bromocriptine should be given as treatment. If the hyperprolactinemia is caused by a pituitary tumor, surgical treatment is required. Other diseases also need to be treated accordingly, taking into account the test results and individual conditions.