How pregnancy tests work

Pregnancy tests work by detecting a hormone called human chorionic gonadotropin (hCG) in the blood or urine. This hormone, also called the pregnancy hormone, is produced when the fertilized egg implants in the uterus. Levels of hCG rise rapidly in the body after this occurs, doubling every 2 or 3 days until they reach a peak around 7 to 12 weeks of pregnancy.

Home pregnancy tests detect hCG in the urine, and doctor's office tests detect hCG in the blood. The more sensitive a pregnancy test is, the lower the levels of hCG it can detect, and the earlier you can tell if you're pregnant. Blood tests can detect smaller amounts of hCG, so they can identify a pregnancy sooner – about 6 to 8 days after you ovulate. Home pregnancy tests can usually detect a pregnancy the day your period is due (about 2 weeks after you ovulate).

To do a home pregnancy test, follow the instructions on the leaflet. Most tests will ask you to hold the test strip in your urine stream or put it in a sample of your urine (collected in a clean, dry cup). After a waiting period (usually 2 to 3 minutes), you will see your results. Results may be displayed in different ways, depending on the test.

If the test says you are pregnant, contact your doctor to schedule an appointment. You may also want to learn more about having a healthy pregnancy. If the test says you are not pregnant but you think you might be, it might still be too early to detect the pregnancy with a home test. Wait at least 3 days (or, if you tested before your period is due, wait until the day your period is due) and test again.