How do pregnancy tests work?

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Pregnancy tests look for a special hormone in the urine or blood that is only there when a woman is pregnant. This hormone, human chorionic gonadotropin (hCG), can also be called the pregnancy hormone.

The pregnancy hormone, hCG, is made in your body when a fertilized egg implants in the uterus. This usually happens about 6 days after conception. But studies show that the embryo doesn't implant until later in some women. The amount of hCG increases drastically with each passing day you are pregnant .

Many home pregnancy tests claim they can tell if you're pregnant on the day you expect your period. But a recent study shows that most don't give accurate results this early in pregnancy . Waiting one week after a missed period will usually give a more accurate answer.


What's the difference between pregnancy tests that check urine and those that test blood? Which one is better?

There are two types of pregnancy tests. One tests the blood for the pregnancy hormone, hCG. The other checks the urine for this hormone. You can do a urine test at home with a home pregnancy test. You need to see a doctor to have blood tests.

These days, most women first use home pregnancy tests (HPT) to find out if they are pregnant. HPTs are inexpensive, private, and easy to use. Urine tests will be able to tell if you're pregnant about 2 weeks after ovulation. Some more sensitive urine tests claim that they can tell if you are pregnant as early as one day after a missed period.

If a HPT says you are pregnant, you should call your doctor right away. Your doctor can use a more sensitive test along with a pelvic exam to tell for sure if you're pregnant. Seeing your doctor early on in your pregnancy will help you and your baby stay healthy.

Doctors use two types of blood tests to check for pregnancy. Blood tests can pick up human chorionic gonadotropin ( hCG) earlier in a pregnancy than urine tests can. Blood tests can tell if you are pregnant about 6 to 8 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. Qualitative hCG blood tests just check to see if the pregnancy hormone is present or not. So it gives a yes or no answer. The qualitative hCG blood test is about as accurate as a urine test.

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