Pregnancy Test Basics

It makes sense to kick off this blog with some information about pregnancy tests.  Whether you do a home pregnancy test or have one performed in a healthcare setting they all test for the same hormone: human chorionic gonadotropin; more commonly referred to as hCG.

The tests that can be done at home are only performed on urine samples.  hCG tests done in healthcare settings may use urine or blood samples.  hCG tests performed on urine simply look for the presence or absence of hCG and give a positive (hCG is present) or negative (hCG is absent) result.  Tests done on blood provide a measurement of the amount of hCG present in the blood.  This type of test is most often done in clinical laboratories.

Many people ask: "How soon in pregnancy will a pregnancy test give a positive result?"  While it's a straightforward question, the answer is surprisingly difficult to determine.  That's because it's difficult to know with certainty precisely when fertilization of the egg occurs and when it gets implanted in the uterus.  hCG is produced after implantation, after which it takes some time for enough hCG to be produced to become detectable in the blood and urine.  Few people would argue that, in most women, a blood test gives a positive result somewhere between 9 and 11 days after fertilization (or about 1 to 3 days before the day of the expected period) and a urine test gives a positive result 1 to 2 days later.


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