A blood test for pregnancy is often used clinically to determine whether a woman is pregnant by measuring human chorionic gonadotropin (HCG) in the serum, and is one of the first methods that can definitively determine whether she is pregnant. After the fertilized egg is laid, the trophoblast cells secrete HCG into the maternal bloodstream and the level rises rapidly, usually 1-fold every 1-2 days, until the peak in the 8th-10th weeks of pregnancy, and then slowly decreases until the stable level in the 18th-20th weeks. Therefore, 8-10 days after the fertilized egg has been laid, a blood test for HCG in the serum can be performed to determine if the egg is pregnant. If you are not sure of the time of ovulation, the test can be done 10 days after the last intercourse, so that the test result will be relatively accurate and the chance of false negatives is low. Generally, serum HCG is less than 5 IU/L in normal people, and if it exceeds 5 IU/L, it indicates the possibility of conception. However, it should be noted that in addition to pregnancy, elevated serum HCG may also be due to some diseases, such as germ cell tumors. Therefore, the diagnosis of pregnancy should be made after 35 days of menopause, and an ultrasound examination should be performed at the hospital to see if there is a round or oval gestational sac in the uterus, and if the HCG doubling is good to make a comprehensive judgment.