Home pregnancy tests have become commonplace. A woman can find out if she is pregnant within minutes and anytime of the day or night. Some tests boast they can detect a pregnancy the first day of a missed period. But how accurate are these tests? Can you really know if you are pregnant the day you should have gotten your period?
Two Types of Pregnancy Tests
There are two basic types of pregnancy tests: blood tests and urine tests. Both tests determine pregnancy by detecting the presence of human chonrionic gonadotrophin (hCG), the hormone that is present in a woman only after an embryo attaches itself to the uterine wall. Once this happens, hCG levels rise quickly and continue to rise each day.
Blood tests must be completed by a doctor and are typically more accurate than urine tests. Blood tests can normally detect pregnancy as early as six to eight days after ovulation. This is because blood tests can detect a very small amount of hCG. A quantitative blood test will measure the exact amount of hCG and is helpful in determining date of conception. A qualitative blood test will simply look for the presence of hCG and give a “yes” or “no” answer.
Urine tests detect hCG when they rise above a certain level. Because of this, they are not normally able to detect pregnancy as early as a blood test can, however they can sometimes detect pregnancy as early as the first day of a missed period. Home pregnancy tests are urine based pregnancy tests.
Accuracy of Home Pregnancy Tests
Most home pregnancy tests are very accurate. Although many home pregnancy tests claim 99% accuracy on the first day of a missed period, a study completed in 2004 [“Pregnancy Tests”, 2006, National Women’s Health Information Center] found only one brand of test (First Response, Early Result Pregnancy Test) consistently detected the small amounts of hCG present that early. Even so, home pregnancy tests are considered accurate, especially when used one week after a missed period.
Using a Home Pregnancy Test
There are several factors that contribute to the accuracy of home pregnancy tests: