What happens when you use an expired pregnancy test?

The most common complication with using an expired pregnancy test is receiving a false negative reading, according to WebMD. Any pregnancy test that is past its expiration date can return a false positive or false negative reading, but the latter is far more likely.

Expired pregnancy tests often lose their ability to register hCG, the hormone that signifies the early stages of a pregnancy, according to BabyHopes.com. Using a pregnancy test past its expiration date typically results in a false negative reading, but false positive pregnancy tests are not uncommon. If the expired pregnancy test has been exposed to heat or moisture, a false positive test can result.