Under normal circumstances, the fetal sac should be inside the uterus after pregnancy. HCG, known as human chorionic gonadotropin, is secreted by the syncytial trophoblast cells of the placental chorion starting 10-14 days after conception. After miscarriage or rupture of ectopic pregnancy, the diagnosis is mostly not difficult; in the early stage of ectopic pregnancy, because the clinical manifestations are not obvious, the clinical examination is mainly used to confirm the diagnosis, such as blood HCG measurement and vaginal ultrasound examination, etc. Blood HCG measurement is crucial to the early diagnosis of ectopic pregnancy. In general, HCG levels in patients with ectopic pregnancy are lower than those in normal intrauterine pregnancies. Clinically, it is difficult to determine ectopic pregnancy based on a particular blood HCG value; in other words, there is no standardized HCG value for ectopic pregnancy, which reflects the risk level of ectopic pregnancy. If the doubling time is greater than 7 days, the possibility of ectopic pregnancy is very high (the doctor will recommend to review the blood HCG value after 3-7 days according to the initial value and consider whether it is an ectopic pregnancy according to the rate of increase of the blood HCG value in the review result); if the doubling time is less than 1.4 days, the possibility of ectopic pregnancy is very low (the review result indicates that the doubling time of the blood HCG value is less than 1.4 days). If the doubling time is less than 1.4 days, ectopic pregnancy is basically not considered). Clinically, the diagnosis of ectopic pregnancy is usually made by combining the blood HCG value with vaginal ultrasound. When the blood HCG is >2000iu/L and the intrauterine fetal sac is not detected by vaginal ultrasound, the diagnosis of ectopic pregnancy is basically established. In conclusion, the diagnosis of ectopic pregnancy needs to combine the results of both blood HCG test and vaginal ultrasound, and cannot rely on blood HCG value alone.