The absence of menstruation for a month may be caused by pregnancy, physiological reasons or pathological reasons. 1. Pregnancy: If you have a normal sex life and do not use contraception, consider pregnancy. After pregnancy, the hormone level in the body rises, and the uterine lining no longer sheds, so there will be a menopause. 2. Physiological reasons: physiological delay is more common in adolescent and perimenopausal women, adolescent women due to the hypothalamus-pituitary-ovary axis development is not particularly mature, there will be menstrual irregularities. 40 years of age or older women enter the perimenopausal period, hormonal changes, menstrual disorders. 3. Pathological causes: Polycystic ovary syndrome will increase the level of androgen in the body, which will affect menstruation and lead to scanty menstruation, low menstrual flow and even amenorrhea. In addition, diminished ovarian reserve function and premature ovarian failure will lead to a fluctuating decline in estrogen levels, affecting menstruation. If you don’t have menstruation for a month, it is recommended that you seek prompt medical attention and treatment.