If there is still no menstrual flow 40 days after miscarriage, first of all, you need to go to the hospital for examination to know what causes it. The most common causes are, first, endocrine disruption of menstruation after miscarriage, which leads to no menstruation, first of all, ultrasound to find out if there are any residues in the uterine cavity, second, you can also find out if there are any adhesions in the uterine cavity or the cervix. If there are adhesions in the uterine cavity and cervix, menstrual flow is already occurring, but the menstrual blood is not flowing out, and it is gathering more and more in the uterus, which can lead to lower abdominal pain in serious cases. Third, ultrasound can also understand the thickness of the endometrium to see if the endometrium is so thin that it prevents menstruation, or if the endometrium is already so thick that it is estimated that menstruation can come in a short time. There is also the possibility of post-abortion polycystic ovary syndrome, which may also lead to lack of menstruation. No matter what the case is, it is important to go to the hospital for examination and decide what kind of treatment will be given depending on what kind of cause.