The blood on the first day of menstruation is black slag is a normal phenomenon. On the first day of menstruation the amount of menstruation is relatively small, due to the small amount of bleeding can not be discharged outside the uterus in time, it will lead to black menstrual blood. Black menstrual blood accompanied by vaginal secretions, discharged outside the body will appear black slag, as long as there is no abdominal pain, vulvar itching and other conditions is generally not to worry. If there is pain in the lower abdomen and itching of the vulva, this may be caused by gynecological inflammation, such as bacterial and fungal vaginitis, as well as pelvic inflammatory disease and endometritis. If there are uterine adhesions, darkening of menstrual blood may also occur. However, a significant decrease in menstrual flow should have a history of uterine operations, etc. If there is an endocrine disorder, such as estrogen deficiency, this can also cause the condition and the volume of menstruation can decrease. If there is black sludge in menstruation, accompanied by reduced menstrual flow or lower abdominal discomfort, you need to promptly go to the hospital for examination and reasonable treatment according to the specific situation, and usually pay attention to vulvar hygiene.