Most pregnancies can be detected if it is 13 days after intercourse during ovulation. When intercourse occurs, the egg and sperm are able to combine normally and develop into a fertilized egg. The fertilized egg will move to the uterine cavity 6-7 days after intercourse to settle, grow and develop, at which time the chorionic villi will form and secrete chorionic gonadotropin, and the chorionic gonadotropin level in the blood will be elevated, which is usually highly suspected as early pregnancy. In addition, in a few cases, if a woman’s ovulation period is delayed or the fertilized egg is slow to develop after formation, the fertilized egg may not be detected 13 days after intercourse because of the short and late movement of the fertilized egg into the uterine cavity. This can help to diagnose pregnancy.