How do pregnancy tests work?

Pregnancy tests look for a special hormone in the urine or blood that is only there when a woman is pregnant. This hormone, human chorionic gonadotropin (hCG), can also be called the pregnancy hormone.

The pregnancy hormone, hCG, is made in your body when a fertilized egg implants in the uterus. This usually happens about 6 days after conception. But studies show that the embryo doesn't implant until later in some women. The amount of hCG increases drastically with each passing day you are pregnant .

Many home pregnancy tests claim they can tell if you're pregnant on the day you expect your period. But a recent study shows that most don't give accurate results this early in pregnancy . Waiting one week after a missed period will usually give a more accurate answer.