How do pregnancy tests work?
All pregnancy tests work by detecting a certain hormone in the urine or blood that is only there when a woman is pregnant. This hormone is called human chorionic gonadotropin (kohr-ee-ON-ihk goh-NAD-uh-TROH-puhn), or hCG. It is also called the pregnancy hormone.
hCG is made when a fertilized egg implants in the uterus. This usually happens about six days after the egg and sperm merge. But studies show that in up to 10 percent of women, implantation does not occur until much later, after the first day of the missed period. The amount of hCG rapidly builds up in your body with each passing day you are pregnant.
Are there different types of pregnancy tests?
Yes. There are two types of pregnancy tests. One tests the blood for the pregnancy hormone, hCG. You need to see a doctor to have a blood test. The other checks the urine for the hCG hormone. You can do a urine test at a doctor's office or at home with a home pregnancy test (HPT).
These days, many women first use an HPT to find out if they are pregnant. HPTs are inexpensive, private, and easy to use. HPTs also are highly accurate if used correctly and at the right time. HPTs will be able to tell if you're pregnant about one week after a missed period.
Doctors use two types of blood tests to check for pregnancy. Blood tests can pick up hCG earlier in a pregnancy than urine tests can. Blood tests can tell if you are pregnant about six to eight days after you ovulate (or release an egg from an ovary). A quantitative blood test (or the beta hCG test) measures the exact amount of hCG in your blood. So it can find even tiny amounts of hCG. This makes it very accurate. A qualitative hCG blood test just checks to see if the pregnancy hormone is present or not. So this test gives a yes or no answer. The qualitative hCG blood test is about as accurate as a urine test.
How do you do a home pregnancy test?
There are many different types of home pregnancy tests (HPTs). Most drugstores sell HPTs over the counter. They are inexpensive. But the cost depends on the brand and how many tests come in the box.
Most HPTs work in a similar way. Many instruct the user to hold a stick in the urine stream. Others involve collecting urine in a cup and then dipping the stick into it. At least one brand tells the woman to collect urine in a cup and then use a dropper to put a few drops of the urine into a special container. Then the woman needs to wait a few minutes. Different brands instruct the woman to wait different amounts of time. Once the time has passed, the user should inspect the "result window." If a line or plus symbol appears, you are pregnant. It does not matter how faint the line is. A line, whether bold or faint, means the result is positive. New digital tests show the words "pregnant" or "not pregnant."
Most tests also have a "control indicator" in the result window. This line or symbol shows whether the test is working properly. If the control indicator does not appear, the test is not working properly. You should not rely on any results from a HPT that may be faulty.
Most brands tell users to repeat the test in a few days, no matter what the results. One negative result (especially soon after a missed period) does not always mean you're not pregnant. All HPTs come with written instructions. Most tests also have toll-free phone numbers to call in case of questions about use or results.
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