Aunt period is rare, just black. What's going on?

Menstruation is rarely black, it is the performance of too little menstruation, too little menstruation is often related to pregnancy, but also need to exclude all kinds of endocrine abnormalities, first to check HCG hematuria, except for the possibility of pregnancy, if necessary, to further exclude ectopic pregnancy, embryo abortion and other special circumstances, except for pregnancy to check female sex hormone six items and thyroid function, except polycystic ovary syndrome, hyperprolactinemia, thyroid dysfunction, premature ovarian failure and other specific endocrine diseases. Except for special circumstances, occasional menstrual flow is too small, sometimes related to female mental and psychological factors, such as exam tension, work pressure, bad mood, sometimes there will be such performance, generally without special treatment, will improve on its own.