Black menstrual periods may occur when the endometrium becomes thin and causes shedding. When the hormone level in the body changes, especially when estrogen is too low, it can cause the endometrial lining to grow slower and cause black menstruation. For example, if you have had multiple abortions or medical abortions, the endometrium may be damaged by the surgical operation, and you may have a black menstrual period. In this case, if possible, the endocrine hormone test, including anti-Müllerian hormone, should be performed on an empty stomach on the second to fifth day of menstruation to determine the function of the ovaries, and depending on the situation, oral medication should be taken to regulate the cycle, for example, progesterone or short-acting contraceptive medication. If it is caused by surgical trauma, hysteroscopy should be done to determine if there is any abnormality in the endometrium, and if necessary, surgical treatment should be performed.