A 13-day delay in menstruation is generally considered abnormal. It is normal for a menstrual cycle to be 7 days early or 7 days late. However, if the period is delayed for 13 days and does not come, it is called irregular menstruation and is abnormal. A delayed period of 13 days may be caused by a variety of reasons. If a woman of childbearing age has a delayed period of 13 days and also has a history of sexual intercourse, the first thing to do is to rule out pregnancy, and an early pregnancy test or blood HCG test can be performed to clarify whether it is pregnancy. If it is determined to be pregnancy, an ultrasound examination should be performed at the hospital in time to rule out the possibility of ectopic pregnancy. If menstruation is often delayed and the amount of menstruation is low, it may be due to endocrine disorders such as polycystic ovary syndrome, hyperandrogenemia, hyperprolactinemia, etc. It may also be due to ovarian hypofunction, which requires prompt medical attention and sex hormone six tests to clarify the cause for active treatment. If a woman usually has a regular period and her period is occasionally delayed for 13 days, it is not necessary to be overly nervous.