The average internal diameter of the gestational sac grows at a rate of approximately 1 mm/d at 5-7 weeks of gestation. The yolk sac is the first structure that can be observed within the gestational sac and its presence is strong evidence of pregnancy. Transvaginal ultrasonography often reveals the yolk sac at 35-37 days of menopause; transabdominal ultrasonography often reveals the yolk sac at 42-45 days of menopause. The normal range of yolk sac diameter is 3-8 mm, with an average of 5 mm. 4. The prognosis is poor if the yolk sac diameter is >10 2000 mm. The prognosis is poor if the yolk sac does not appear, is less than 3 mm, is deformed, or has strong internal echogenicity. (1) Embryonic abortion can be diagnosed if the embryo is ≤5 mm in length, without heart tube pulsation and still without heart tube pulsation after 7-10 days; (2) Embryonic abortion can be diagnosed if the embryo is >5 mm in length, without heart tube pulsation or the average internal diameter of the gestational sac >20 mm, without yolk sac and embryo; (3) the average internal diameter of the gestational sac ≤20 mm, without yolk sac and embryo, at 1-2 weeks. (3) the average internal diameter of the gestational sac is ≤20 mm without yolk sac and embryo, and the absence of yolk sac and embryo after 1-2 weeks can be diagnosed as embryonic abortion. (2) Transabdominal ultrasonography: (1) Embryonic abortion can be diagnosed if the embryo is ≤9 mm in length, without heart tube pulsation and still without heart tube pulsation after 7-10 d; (2) Embryonic abortion can be diagnosed if the embryo is >9 mm in length, without heart tube pulsation or the average internal diameter of the gestational sac is >25 mm, without yolk sac and embryo; (3) The average diameter of the gestational sac is ≤25 mm, without yolk sac and embryo, and still without yolk sac and embryo after 1-2 weeks. (3) The absence of yolk sac and embryo, and the absence of yolk sac and embryo after 1-2 weeks of rechecking can be diagnosed as embryonic arrest. The blood HCG is 1500~1800u/l and the gestational sac is visible on ultrasound. In multiple pregnancies, blood HCG is ≥6000~6500u/l and the gestational sac is visible on abdominal ultrasound. Blood HCG ≥3000u/l in multiple pregnancies can be distinguished by ultrasound. The diagnosis of ectopic pregnancy is basically established when the blood HCG is ≥2000u/l and the intrauterine pregnancy is not visible on ultrasound.