Menstruation is affected by a variety of factors, 18 years old ovarian function has been stabilized in most cases, 2 months without menstruation to rule out pregnancy, but also consider menstrual irregularities, such as polycystic ovary syndrome, hyperprolactinemia, etc., but also to rule out pituitary tumors, endocrine abnormalities, and so on. When menstruation is delayed, if you have sex with a woman, first do the early pregnancy test to rule out the possibility of early pregnancy, check positive not to menstruate because of pregnancy. When the test is negative, the common reasons for delayed menstruation such as stress, staying up late, emotional tension, anxiety, malnutrition, cold, taking certain medications, environmental changes, etc. Occasionally delayed for 2 months you can go to the hospital to do ultrasonography to see the thickness of the endometrium, and under the guidance of the doctor to regulate. If you do not have your period for 3 consecutive months, consider amenorrhea, and if necessary, take medication to promote menstruation and regulate under the guidance of a doctor.