For women who have not had sex and have lost their periods after half a day, consider that it is not a normal manifestation of menstruation at all, but an abnormal uterine bleeding, such as the common anovulatory type of menstruation. This is because a woman does not ovulate and her body does not secrete progesterone. The stimulation of a single estrogen may lead to a small amount of endometrial peeling, causing a half-day period. For women who are sexually active and have a half-day period, the first thing to consider is abnormal vaginal bleeding due to pregnancy, and you need to consider checking blood HCG or testing with early pregnancy test strips. For women who have had an abortion, abnormalities due to endometrial adhesions should also be considered and an ultrasound must be checked to confirm the diagnosis.