What is the reason for a small amount of dark blood during menstruation?

Patient's question:

Not normal, came early, also pushed later, the color of those who came is black, long time, but few

Doctor's answer:

Irregular menstruation is a common gynecological disorder. It is characterized by abnormal menstrual cycles or bleeding volume, or by abdominal pain and systemic symptoms during the premenstrual period or menstrual period. The cause may be organic lesions or functional disorders. Blood diseases, hypertension, liver disease, endocrine diseases, miscarriage, ectopic pregnancy, molar pregnancy, reproductive tract infections, and tumors can all cause menstrual disorders. In traditional Chinese medicine, it is generally related to the liver, and treatment is usually based on the Siwu Decoction as the foundation formula, with modifications.