The HCG doubling time in normal intrauterine pregnancy is 1.7-2 days in early pregnancy, and the HCG value is about 50,000-100,000 U/L in 8-10 weeks of gestation, then the HCG decreases, and the HCG is only 5,000-10,000 U/L in mid to late pregnancy. regular monitoring of serum HCG value is clinically important for the differential diagnosis of intrauterine pregnancy and ectopic pregnancy. Generally, HCG values in patients with ectopic pregnancy are lower than intrauterine pregnancy, and HCG doubling time greater than seven days may be ectopic pregnancy. Combining serum HCG, serum progesterone, and ultrasound is helpful in diagnosing ectopic pregnancy. If the serum progesterone is less than 25ng/mL, the serum HCG value is greater than 2000U/L, and no gestational sac is seen in the uterine cavity on vaginal ultrasound, ectopic pregnancy is generally considered a possibility.