Pregnancy tests work by detecting the hormone human chorionic gonadotropin (hCG), which is produced during pregnancy. When a fertilized egg attaches to the lining of the uterus, the body starts producing hCG. This hormone can be detected in urine or blood approximately 10 to 14 days after conception. Modern home pregnancy tests typically use a technology called a lateral flow device. When urine is applied to the test strip, it flows through the strip and interacts with antibodies coated on latex microbeads that specifically bind to hCG if it is present. If hCG is detected, a visible line or symbol (such as a plus sign) appears on the test strip indicating pregnancy. If no hCG is present, only the control line appears, indicating a negative result. Blood tests for pregnancy, done in a medical setting, can detect hCG earlier and measure the exact amount of hCG in the blood, which can be helpful for monitoring pregnancy or diagnosing certain conditions. Home urine pregnancy tests are about 99% accurate when used properly, and the best time to take the test is after a missed period to reduce the chance of a false-negative result. Early morning urine is preferred for urine tests since it contains higher concentrations of hCG. In summary, pregnancy tests detect the presence of hCG hormone in urine or blood to determine if a woman is pregnant.