How early can you test for pregnancy?

You've decided you're ready to start a family, and you want it to happen right away. Finding out if you're pregnant is an exciting process, but waiting for it to happen can really try a person's patience. Just how soon after having sex can you find out if you're pregnant?
You're pregnant when an egg is fertilized by a sperm cell. However, it's nearly impossible to tell you're pregnant the instant it happens because pregnancy is only detectable when it starts producing the hormone human chorionic gonadotropin (hCG). And this doesn't happen until the fertilized egg attaches to the wall of your uterus. For some women, that could take up to six days, and in others it doesn't happen until after a missed period. In other words, it seems to take an eternity.
After the egg's implanted in your uterine lining, your body starts producing hCG. In early pregnancy, the amount of this hormone doubles every two or three days. The presence of this hormone in your urine is what tells you you're pregnant.
Two types of pregnancy tests can help you determine if you'll soon welcome a new addition to your family:
Urine test: With this method, urine has to come into contact with a special stick. You either urinate directly onto the stick or dip it in a cup of your urine. After a few minutes, an indicator on the stick will register whether you're pregnant. Generally, you can take this test as soon as you've missed your period, though some tests can be taken sooner.
Blood test: There are two kinds of blood tests: qualitative hCG and quantitative hCG, also called a beta hCG test. You can take these within seven to 12 days of conception, which means you can test sooner than a urine test [source: American Pregnancy Association]. However, results take longer to get. With a blood test, your doctor will take a blood sample. The qualitative hCG test detects the presence of the hormone in your blood; the quantitative hCG test measures the precise amount.
To take a pregnancy test, you can see your doctor or you can purchase one to take one at home. A doctor's test will give you an accurate result, but a visit may be expensive. Home pregnancy tests are less expensive, and when taken correctly, can deliver quite accurate results. Additionally, they offer the bonus of taking them in the privacy of your own home.

Accuracy of Pregnancy Tests

While a blood test is the most reliable way to find out if you're pregnant, home pregnancy tests can also be very accurate -- if you use them correctly. Follow the instructions to the letter and don't use an expired test.
You may also want to take some of the tests' claims on how quickly they work with a grain of salt. Home pregnancy tests can't always detect low levels of hCG, so if you take a test right away, you may not get an accurate result. Waiting at least until you miss your period allows levels of the hormone to build up enough for the test to detect them, and some women may need to wait until a week after a missed period for best results.
Keep in mind that your body doesn't start producing hCG until the fertilized egg implants itself in the uterine lining. Exact ovulation and implantation dates vary by woman. It's quite possible that you could miss a period and be pregnant, but not yet be producing hCG. In that case, a pregnancy test won't work.
Pregnancy tests may also produce false positives and negatives. False positives are extremely rare, but they can happen in the following situations:

• You were recently pregnant.
• You take medicine containing hCG.
• You have blood or protein in your urine.
• You have ovarian cysts or an ectopic pregnancy.
• You're going through menopause

False negatives can be more common, and many false negatives are due to these user errors:

• The test is past its expiration date.
• You're taking the test too soon.
• You didn't follow the instructions. The test needs time to work, but if you give it too much time, you may get the wrong results.
• Your urine is diluted. Take your test when you get up and your urine is its most concentrated.

If you test yourself and get results you don't think are right, wait a few days and take another test. If the results are mixed or you don't get your period, see your doctor, who can do a blood test or discover other factors that may be contributing to a missed period. Irregular periods may also be partly to blame for erroneous test results.

If you suspect you're pregnant, chances are you're considering taking a home pregnancy test. And why not? They're readily available, easy to use, and can buy you peace of mind — not to mention quick results!
But before you head to the pharmacy to buy a home testing kit, learn the answers to some basic home pregnancy test questions from the National Women's Health Information Center.

How soon after conception is a pregnancy test effective?

Pregnancy tests, which are regulated by the Food and Drug Administration, have come a long way since the early to mid 1900s when toads, rats, and rabbits were actually used in testing. Today, over-the-counter home pregnancy kits provide privacy and fast results. They can detect pregnancy as soon as six days after conception or one day after a missed menstrual period. This is a major advantage in allowing women to seek the earliest prenatal care possible.

How do pregnancy tests work?

Pregnancy tests detect the presence of a hormone produced by pregnant women after conception, called human chorionic gonadotropin (hCG). In the 1970s, a method called ring or tube agglutination testing used a test tube containing prepackaged red blood cells to detect hCG in urine. If a ring showed at the bottom of the tube after addition of a urine sample, the test was positive. These tests are very sensitive to movement and human error so they're rarely used today.
The test kits you find in your drugstore today are much more sophisticated. Brands such as e.p.t. and First Response contain special antibodies that detect minute traces of hCG in urine. The antibodies are molecules coated with a substance that bonds to the pregnancy hormone if it's present. The tests are easy to use: A urine sample is combined with the antibodies in a special container and the test is timed. A color change indicates a positive or negative result.
Products such as Clearblue Easy use a testing method called "rapid assay delivery," which can give results in only three minutes and even inform the user if the test hasn't been done properly. This method combines a biochemical process with antibodies that detect hCG in a pen-shaped instrument.

How accurate are home pregnancy tests?

Although most manufacturers claim that home pregnancy tests are 99 percent accurate, inaccurate results may be more frequent due to improper usage, use of a product past its expiration date, exposure of the test to sunlight, and the presence of cancer in the user. It's very important to follow the package instructions exactly for results to be accurate.
Regardless of the brand used or result obtained, most manufacturers recommend repeating the process a few days later to confirm results, because levels of hCG following conception are so low. The strength of each test varies, and the test may not pick up the amount of hCG hormone present the first time you test.
You should definitely make an appointment to see your doctor as soon as you think you're pregnant. It's important to get prenatal care as early as possible, for your sake and for your baby's.