HCG is also known as human chorionic gonadotropin. When HCG reaches 2,000-3,000 mIU/mL, the pregnancy sac can be seen through vaginal ultrasound. On the 6th day after the fertilization of the sperm and the egg, the trophoblast cells start to secrete HCG, and on the 10th day after the fertilization, the pregnancy can be detected through a blood test in the hospital. The HCG in the pregnant woman’s body doubles in size every two days, and shows a phenomenon of doubling in size every other day, and when the HCG reaches 2,000 – 3,000 mIU/mL, the gestation sac can be seen through vaginal ultrasound examination. According to the growth of HCG, the growth and development of the gestational sac can be roughly assessed. The phenomenon that HCG does not double every other day suggests that the embryo is underdeveloped or ectopic pregnancy is possible. After the pregnancy is confirmed, you should have regular checkups to see how the fetus is developing in the uterus.