All over-the-counter home pregnancy tests work in very much the same way. Pregnancy tests test for the presence of the hormone hCG, also known as human chorionic gonadotropin. This hormone is not present in a woman’s system, at least not in measurable amounts, until the fertilized egg has implanted itself into the woman’s uterus. By the time that a woman has missed a period, her levels of hCG should be high enough that just about any home pregnancy test will be effective at being able to detect it, and to give the woman a positive pregnancy result. Having said that, the fact of the matter is that not all pregnancy tests are equally effective at detecting pregnancy in the earlier stages of pregnancy.

Home pregnancy tests can vary greatly in terms of their sensitivity. Some tests are very sensitive. These especially sensitive tests will be able to measure levels of hCG that are as low as 25 milli-International Units per Milliliter, or 25 mIU/ml. For other tests, their sensitivity level is going to be much higher. Some tests won’t register levels of hCG that are below 150 MIU/ml, and some go up as far as 250 mIU/ml in terms of their sensitivity.

If a pregnancy test is more sensitive, it is going to be more effective at detecting a pregnancy earlier than a test that is not quite as sensitive. For some women, a sensitive test might be able to confirm whether or not they are pregnant as early as 10 days after they ovulate. The tests that are not as sensitive would not be able to confirm whether or not a woman is pregnant until much later, perhaps even as many as 20 days after they ovulate.

For the most part, unless you have been trying to conceive and you are anxious to know whether or not your attempts have been effective, almost any given pregnancy test that is taken after you have missed your period should be equally effective. If you need to know sooner, however, you will need to use the more sensitive tests.

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