If the menstrual flow is low once in a while, and if there is a history of sexual intercourse, there is a possibility of biochemical pregnancy. Biochemical pregnancy means that the sperm and the egg have already united, but when they enter the uterine cavity, they are discharged out of the vagina together with the menstrual blood, and the possibility of pregnancy is often overlooked in clinics and considered to be a decrease in the menstrual flow, which is ignored and not detected in clinics in which biochemical pregnancies occur in many women. It is also possible that increased stress and poor rest at the time of menstruation or before menstruation can lead to decreased menstrual flow, or drinking too many frozen drinks can also lead to decreased menstrual flow.