Pregnancy tests are designed to tell if your urine or blood contains a hormone called human chorionic gonadotropin (hCG). This hormone is produced right after a fertilized egg attaches to the wall of a woman’s uterus.
This usually happens — but not always — about six days after fertilization. If you’re pregnant, levels of hCG continue to rise rapidly, doubling every two to three days.
Two main types of pregnancy tests can let you know if you’re pregnant: urine tests and blood tests.