The first thing to consider is that the bleeding is caused by ovulation, or may be caused by uterine adhesions, polycystic ovary syndrome and other diseases. 1. Ovulation bleeding: Fluctuations in estrogen and progesterone levels during ovulation can cause a small amount of endometrial shedding, which can result in a small amount of vaginal bleeding. This may be mistaken for the onset of menstruation, which may occur one day after the onset of menstruation. 2. Uterine adhesions: The absence of menstruation for one day may also be due to uterine adhesions. Uterine adhesions can be caused by endometrial trauma, infection, low estrogen levels and other factors. Patients may experience abnormal menstruation and abdominal pain, which may be manifested as decreased menstruation or even amenorrhea. 3. Polycystic ovary syndrome: The cause of polycystic ovary syndrome is not yet clear, and it may be due to a combination of genetic and environmental factors. Symptoms of patients are scanty menstruation, scanty menstruation, amenorrhea, which may be manifested as having one day of menstruation and then no more. There are many reasons for the absence of menstruation in one day. If physiological factors are excluded, patients need to identify the cause of the disease in time.