If the usual menstrual cycle is very regular, about 28 days once, 17-year-old girls have delayed menstruation: 1, during sex, did not do a good job of contraception, there may be pregnancy, it is best to use test paper or come to the hospital to draw blood test HCG, to exclude the case of unwanted pregnancy. 2, if completely ruled out pregnancy or still no sex, may be caused by endocrine disorders, if the recent period If the mental stress or often stay up late, irregular work and rest time, change of environment, etc., may affect ovulation or even inhibit ovulation, resulting in delayed menstruation. If the thickness of the endometrium is moderate, you can inject progesterone injection and take progesterone capsules to promote menstruation. If the menstrual cycle is usually very disordered, it is recommended to take a blood test for endocrinology on the third day of menstruation to see if there is polycystic ovary syndrome.