A pregnancy test is a medical test that is used to determine whether or not a woman is pregnant. These tests work by detecting the presence of a hormone called human chorionic gonadotropin (hCG) in a woman’s urine or blood. This hormone is produced by the placenta after a fertilized egg has implanted in the uterus. Pregnancy tests are highly accurate when used correctly, and most can detect hCG levels in the urine or blood as early as a few days after a missed period. Home pregnancy tests are widely available and can be purchased without a prescription, while more sensitive tests that are administered by a healthcare professional can detect hCG levels even earlier in the pregnancy.