How Does a Pregnancy Test Work?

Pregnancy tests detect something called Human Chorionic Gonadotropin (hCG). Simple right? I mean who doesn’t know what Human Chorionic Gonadotropin is? Well I didn’t, and maybe you don’t either, so let’s find out.

Human – Not a dog, an Oak Tree, a Transformer, or any other space creature. The following diagram should help.

Human and not human

Chorionic – This one’s unfamiliar for sure. The root word here is “chorion” which refers to the outer membrane surrounding a developing embryo. Embryo describes a stage of human development, just like infant, toddler, or adolescent, and refers to a human in their first eight weeks of development. After eight weeks the growing baby is called a fetus, and we’re called infants or newborns on our birthday. So chorionic refers to something that comes from the chorion.


This is not Gonadotropin.

Gonadotropin – This is a specific type of hormone. Think about it like this, Bulldog is to dog what Gonadotropin is to hormone.

Putting it all together, Human Chorionic Gonadotropin (hCG) simply means a hormone produced as a human embryo (baby) develops.

Pregnancy tests work on a chemical level, using a kind of molecular magnetism. The test contains a molecule with some color in it that is designed to attach itself to hCG, and when it finds the hCG the color is released and it shows up in the tiny window on the pregnancy test.


hCG increases as the baby grows, so the reliabilty of the test is better two weeks after conception than it would be just one week after. This is why a test that shows “not pregnant” may actually be inconclusive because the hCG levels may be too low to show up on your test. If you’re in doubt you should schedule an appointment with your doctor.

Bulldog Image courtesy of Photostock /

Share this:

We’d Love To Talk With You

Join PHI Center Online:


Latest From the Blog

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

Facebook Updates