The first menstruation is the first physiological bleeding from the uterus at the age of maturity in adolescent females and is a sign of sexual maturity. It usually occurs between the ages of 13-15 years old, 11-12 years old in the early case, and 17-18 years old in the late case. How to judge the blood of menarche is menstruation, can specifically refer to the following points: 1, age: women over 10 years old, if there is no vaginal inflammation, trauma, the vaginal bleeding that occurs at this time, it is likely to be the onset of menstruation; 2, the duration of bleeding and the amount of bleeding: menstrual bleeding duration is generally in the range of 3-7 days, the amount of bleeding in the range of 20-80 ml, an average of 50 ml, which is the second day, the third day of the bleeding of the largest amount of money; 3. Menstrual symptoms: during menstruation, due to pelvic congestion, menstrual symptoms such as dizziness, abdominal pain, lumbago, breast swelling and pain may occur; 4. Auxiliary examination: ultrasound examination of the uterus and ovaries during vaginal bleeding is the most reliable criterion for determining the onset of menstruation, and it can also exclude bleeding caused by other diseases. The lateness or early onset of menarche is affected by various internal and external factors, such as nutrition, health condition, race, heredity and climate. Those who are weak or malnourished may be late, while those who are strong and well nourished may have early menarche. After menarche, most people have irregular menstruation, which may last for several months to a year, which is normal and not a cause for concern.