Taking a Pregnancy Test

How does a test tell if you are pregnant or not?
A pregnancy test detects the presence of a hormone called human chorionic gonadotropin (hCG) in your blood or in your urine. hCG is produced in the placenta shortly after the embryo attaches to the uterine lining and builds up rapidly in your body in the first few days of pregnancy.

How long do I have to wait before I take a test?
Most doctors recommend that you wait until the first day of your missed period, which is one of the first signs of pregnancy, before taking a home pregnancy test. This is usually around two weeks after conception. However, some tests are more sensitive (and more expensive) than others and can be taken earlier. Concentrations of hCG are reported in milliInternational Units (mIU) or amounts equal to 1/1000th of an IU per milliliter. A pregnancy test with a sensitivity of 20 IU/L is more sensitive than one with 50 IU/L.

A blood test administered by your doctor is more sensitive than the early home tests and can be taken between 7 and 12 days after you conceive. (It is possible that these tests can be done too early and show a false negative result.) If you receive a negative result and still do not start your period, another test should be done.

How accurate are home tests?
Home tests are very accurate (around 97%) when used correctly. Some kits come with two tests because mistakes can happen.

If you take a test too early, you may get a false negative (when the test says you are not pregnant but you are). Your body needs time for the hormone to rise to a high enough level to be detected in a test. If the test comes back negative but you still think you could be pregnant, wait a few days and try again.

False positives (when the test says you’re pregnant but you’re not) are possible, but rare. A positive pregnancy test is a pretty good indication that you are pregnant.

Last updated: 02/2020