Home Pregnancy Tests
The home pregnancy test has become the typical first step for women who think they may be pregnant. Pregnancy tests work by measuring the levels of human chorionic gonadotropin (hCG), a hormone that is produced by the placenta during pregnancy.
Many tests claim 99% accuracy in clinical studies. But how accurate are they, really?
Pregnancy tests vary in their sensitivity, or how much hCG is needed to trigger a positive result. In early pregnancy, the concentration of hCG in a woman’s urine can double every two or three days! For a 95% accurate result on the day of missed menses, a test must be sensitive to 12.5 mIU/mL. According to one study, only 16% of tests were accurate one or two days after a missed period. ((Cole LA, Khanlian SA, Sutton JM, Davies S, Rayburn WF (2004). Accuracy of home pregnancy tests at the time of missed menses. AJOG, 190(1):100-5.)) However, highly sensitive tests are often more prone to false positives. Typically, it is better to wait one week after missing a period to take a home pregnancy test, at which time a sensitivity of 100 mlU/mL should be sufficient.
Each pregnancy test will come with specific instructions for how it is to be used and how and when the results are to be interpreted. Test types vary from cassettes and strips that display colored lines to tests with digital read-outs. A recent study showed that women misread cassette and strip tests 30 to 40% of the time. ((Pike J, Godbert S, Johnson S (2013). Comparison of volunteers’ experience of using, and accuracy of reading, different types of home pregnancy test formats. Exp Opin Med Diagn, 7(5):435-41.)) Tests with digital displays are much easier to read and use, but are usually a bit more expensive.
Quick Home Test Tips
- Follow the instructions for taking the test and reading the results exactly.
- Taking a home pregnancy test with the first urine of the morning will yield the best results. The longer the urine used for your pregnancy test has been in your bladder, the better.
- Do not drink a lot of extra water immediately before taking a pregnancy test, as extra fluids could over-dilute the urine.
- For best results, home pregnancy tests should be taken 5 to 7 days after missing a period. Be sure to check the sensitivity of the test that you are using.
It is best to get confirmation of pregnancy from a medical professional. A home pregnancy test can only indicate hormone levels, not confirm that you are pregnant or that you have a pregnancy that will develop. An ultrasound exam is the best and fastest method to confirm a viable pregnancy.