A blood test in the early stages of pregnancy can detect pregnancy, but it can only be highly suspicious and not confirm a normal intrauterine pregnancy, and the blood test can also be elevated in case of trophoblastic disease. Usually, after intercourse during ovulation, the egg and sperm can unite and develop into a fertilized egg. About 6-7 days after intercourse, when the fertilized egg is transplanted to the uterine cavity and takes up residence, the corpus luteum of the ovary will secrete chorionic gonadotropin, so the chorionic gonadotropin level in the blood test will increase. If the chorionic gonadotropin level rises above 10 IU/L, early pregnancy is usually highly suspected. An elevated HCG level generally only proves the possibility of pregnancy, but cannot determine whether it is a biochemical pregnancy, ectopic pregnancy or intrauterine pregnancy.