Emergency contraception is a remedial measure taken within a short period of time after an unwanted pregnancy is detected. Generally, there are two ways, namely intrauterine device and oral emergency contraceptive pill, but both methods have the possibility of contraceptive failure, and it is clear whether emergency contraceptive failure occurs through symptoms and auxiliary examination in the clinic. 1. Judgment of emergency contraceptive failure 1. Judgment by symptoms (1) No withdrawal bleeding about one week after taking emergency contraceptive pill; (2) The next menstrual period is more than one week away, followed by early pregnancy reaction such as nausea, vomiting, weakness, acidity and spicy food. (2) Judgment by examination The next menstruation is delayed, and the early pregnancy test or blood HCG test is positive. The reasons for failure of emergency contraception 1.Pregnancy before taking remedial measures; unprotected intercourse again or continuously after taking remedial measures; 2.The first time to take the emergency contraceptive pill for more than 72 hours, or the interval between two doses is more than 12 hours; 3.The birth control device is placed only after 5 days of unprotected sex; 4.The emergency contraceptive pill and some antibacterial and anti-tuberculosis drugs are taken at the same time, which can affect the efficacy of the pill; 5. Fever, vomiting, etc. can affect the efficacy of the pill; 6, the emergency contraceptive pill as a regular contraceptive pill is often used. Third, emergency contraception precautions 1, it is recommended to take emergency contraceptive pills after meals or before bedtime, can reduce nausea, vomiting and other adverse reactions; vomiting occurs within 2h after taking the pill, should immediately take the same dose of emergency contraceptive pills, while taking antiemetic drugs to avoid contraceptive failure; 2, emergency contraceptive pills are only effective for an unprotected sex, and the drug hormone dose, side effects are also large, should not be repeated long-term use; 3, after using emergency contraceptive methods. 3.After using emergency contraceptive methods, the next menstrual period is still coming after more than 1 week, a pregnancy test should be performed in time to determine whether it is a failure of emergency contraception; 4.Placement of birth control ring within 5 days after unprotected sex; 5.After taking emergency contraceptive pills orally, avoid unprotected sex during this menstrual cycle.