How Do Pregnancy Tests Work?

2. Question: How Do Pregnancy Tests Work?

Answer: A pregnancy test (hpt) functions by detecting a unique hormone that is produced by the placenta (which surrounds the developing embryo). The "pregnancy" hormone is called hCG and because it is made by the placenta, its the perfect natural "marker" to determine if a baby is on board.

Once in a woman's circulatory system, hCG will accumulate in urine. And once the amount of hCG in a urine sample reaches a certain volume, a pregnancy test will signal a positive result, alerting you to the fact that you have successfully achieved a pregnacy! Note: Home test kits involve urine samples; your doctor may also use a blood hCG test to confirm a pregnancy. hCG blood tests can also provide you with an hCG "quantity" or number. Urine tests operate like a light switch - they are either on or off.

A pregnancy test functions because of a special reagent that reacts and binds to hCG. As urine and testing dye move across a pregnancy test reagent field, hCG is captured along with the dye to produce a "test sign" or positive test line. Very few things can interfere with a pregnancy test (typically, only hCG-containing fertility drugs can precipitate erroneous results).

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