When the sperm and egg combine to form a fertilized egg, it runs through the fallopian tube and reaches the uterine cavity in about a week, where it will be deposited. At this time, the trophoblast cells of the embryo will secrete chorionic gonadotropin, which can be detected in a woman’s blood about a week or so after fertilization. It can be detected in the woman’s blood about one week after fertilization, but can only be detected in the urine about half a month after fertilization. Since the concentration of hormones is lower in urine, it is recommended that the test be done in the first urine after waking up as the results are more accurate because the hormone content in urine is higher at this time.