Pregnancy tests measure the hormone human chorionic gonadotropin, most commonly called hCG. HCG is produced when a fertilized egg implants in the uterus and appears in the blood and urine of pregnant women as early as 10 days after conception. It is also called the pregnancy hormone.
Types
There are two types of pregnancy tests, and both have been shown to be accurate when used correctly and at the correct time. A home pregnancy test is an inexpensive option that tests for hCG in the urine. Tests that measure for hCG in the blood must be done at your doctor's office. There are two varieties of blood tests, quantitative and qualitative. Quantitative tests measure the amount of hCG in the blood, while qualitative tests measure only for presence of hCG in the blood. The National Women's Health Information Center asserts that quantitative blood tests are the most accurate pregnancy test.
Function
Pregnancy tests are performed primarily for three reasons. First, and most commonly, to determine if a woman is pregnant. Secondly, to diagnose medical conditions that may cause an abnormal increase in production of hCG. The third function applies only to quantitative blood tests. These tests may be used to monitor the development of the pregnancy through the first trimester--approximately the first three months.
Time Frame
The American Pregnancy Association states that most doctors recommend waiting until the first day of your missed period to use a home pregnancy test to increase the likelihood of accurate results. This is typically the first sign of pregnancy and comes approximately two weeks after conception. Blood tests administered by physicians are more sensitive than even the earliest home pregnancy tests. They can be taken 7 to 12 days after you conceive--significantly before your missed period.
Considerations
Home pregnancy tests are approximately 97 percent accurate when used correctly, according to the American Pregnancy Association. Taking a test too early may produce a false negative, when the test says you are not pregnant but you are. If you get a negative test result but believe you are pregnant, wait a few days for the hormone levels to rise and then test again. False positives, when the test says you are pregnant but you are not, are rare.
Warning
Some medicines used to treat infertility have hCG in them and can thus produce false positive test results. If you have any concerns about your pregnancy test results, see your doctor for a blood test and pelvic exam for confirmation. It is important to begin medical care as early as possible to work toward a healthy pregnancy and baby.
