What’s in a pregnancy test?

By July 31, 2018 Pregnancy Q&A

Many women have taken a pregnancy test. But what is being tested when you pee on a stick? Is it a hormone? Is it a chemical, like estrogen or progesterone, or maybe testosterone if the baby is a boy?

The urine pregnancy test is looking for a chemical called beta hCG. This is actually secreted by the embryo.  The beta hCG then passes into the mother’s bloodstream and is eventually filtered through the kidneys. From the kidneys, the chemical passes in the urine. Hence, it can be detected in the urine and in the blood. Except in rare cases, a positive beta hCG in the urine or blood means that a woman is pregnant.

When we (or you) test in the urine it gives only a “negative” or “positive” result. There’s no number attached to it. The blood test is measuring the same chemical but it gives a number.  In a normal pregnancy, the beta HCG should double every 48 hours most of the time. This is why we test it more than once in some patients. Depending on whether it is going up, down, or staying the same, the beta hCG gives alot of information about a pregnancy in the early stages.

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