If you still have black blood on 7 days of your period, you have to consider that it may be an abnormal manifestation due to a prolonged menstrual period, or due to an abnormal cervix. However, for women with black blood on 7 days of menstruation, then it is also important to rule out that it may be abnormal vaginal bleeding due to pregnancy and not a true menstruation. Therefore, after this happens, you should go to the gynecology department of the hospital and check the pelvic ultrasound, gynecological internal examination, and blood HCG to determine the specific cause. For women with abnormally high blood HCG, it can be judged that it is not a real menstrual flow, but an abnormal uterine bleeding caused by pregnancy, which may be a symptom of pre-eclampsia or an ectopic pregnancy, so it is necessary to combine with ultrasound to make a judgment, and if necessary, regularly recheck the blood HCG to determine the development status of the gestational sac. If the blood HCG is not pregnant and the ultrasound reveals that the endometrial lining is too thick, it may be caused by ovarian endocrine disorder, and a sex hormone test is needed to confirm the diagnosis.