Pregnancy tests work by detecting the human chorionic gonadotropin (hCG) hormone

Pregnancy tests work by detecting human chorionic gonadotropin (hCG). hCG is a hormone found only in pregnant women. It is produced by cells in the uterus and is responsible for signaling the ovaries to produce estrogen and progesterone to help your fetus grow. hCG levels continue to rise as your pregnancy progresses. Both urine and blood pregnancy tests can detect hCG.

There are two main types of pregnancy tests: urine and blood. Both are commonly used to detect pregnancy.

The urine pregnancy test

The urine pregnancy test is one of the most popular ways to detect pregnancy. It works by detecting levels of hCG in the urine. Home pregnancy tests are actually urine tests that can be performed in the privacy of your own home. There are a wide variety of urine pregnancy tests available on the market today. Each test ranges in sensitivity, with some urine tests being able to detect hCG levels as low as 15 ml/u.

• Performing a Home Pregnancy Urine Test
  A home pregnancy test is pretty easy to perform, though each test varies in the procedure. Be sure to read the instructions included with the test before you use it. Also, check to make sure that the expiration date hasn’t passed. Most urine tests come with a testing strip which, when exposed to urine, detects the presence of hCG. Make sure to read the directions on the packaging, but typical instructions for performing a home pregnancy urine test are the following

1. Remove the test strip from the package. 
2. Insert the test strip in your urine stream or dip the strip into a cup of urine (follow the instructions on the box). 
3. Wait for the indicated time (usually a minute or two). 
4. The test strip should have changed colors or be displaying a symbol that alerts you to whether you are pregnant or not.

The blood pregnancy test

Pregnancy blood tests are performed at your doctor’s office or health clinic. They detect pregnancy by measuring hCG levels in your blood. There are two types of pregnancy blood tests:

1. Quantitative Blood Test
   The quantitative blood test detects pregnancy by measuring the exact amount of hCG in your bloodstream. It can also be used to detect how far along you are in your pregnancy.
2. Qualitative Blood Test
   The qualitative blood test detects pregnancy by indicating the presence of hCG in your blood. It does not measure your hCG levels and only provides a yes or no answer as to whether or not you are pregnant.

• Performing a Blood Test
  Blood pregnancy tests are performed by health care professionals in an office or a clinic. It is just like a simple blood test.

1. A spot on your arm will be cleaned with alcohol. 
2. A needle is inserted into your arm.
3. Blood is drawn from the needle into a little tube. 
4. The tube is sent to a laboratory where it will be tested. Pregnancy test results typically take a day or two.

Pregnancy test accuracy

The accuracy of pregnancy tests has improved over the years. Both urine and blood pregnancy tests are surprisingly accurate – in fact, they claim to produce results that are 97% to 99% accurate. Of course, mistakes can happen and it accuracy often depends on how the test was performed.

• Home Pregnancy Tests Accuracy
  Home pregnancy tests are usually about 97% accurate, but this varies from brand to brand. In order to get the most accurate results, it is a good idea to wait for about a week after your period is due before testing. This allows more hCG to build up in your urine, which will allow for a more accurate test. Some urine tests can be used on the first day that your period is due, however, it is unlikely that you will achieve that 97% accuracy rate if you test so early. It is best to perform a urine test in the morning before you drink or eat. This will allow for a buildup of any hCG in your urine.
• Clinic Tests Accuracy
  Blood tests performed at your clinic have a 99% accuracy rate and can detect pregnancy earlier than most urine tests. Blood tests can be performed 7 days after you ovulate (which is about a week before your period is due) and still provide accurate results. Sometimes, lab oversights can affect the accuracy of results, however, this is rare.

False-positive and false-negative results

It is possible to receive false results, both positive and negative, from your urine or blood pregnancy test.

• A false positive pregnancy result is a result that is positive when in fact you are not pregnant. 
• A false negative pregnancy result is a result that is negative when in fact you are pregnant. 

If you get a false positive from a home pregnancy test, it is usually the result of faulty test strips. Most home pregnancy tests now have an indicator that shows whether or not the test is working correctly. If you leave your pregnancy test too long before checking it, this can also cause a false positive. Eventually, the urine will soak through the test, exposing the chemical strip that indicates pregnancy. Be sure to follow the instructions as closely as possible.

Both blood and urine tests can also produce false positives if you are taking a drug that contains hCG. These drugs are commonly used in fertility treatments, so ask your health care provider about whether your medications could affect pregnancy test results.

False-negative pregnancy tests are also possible and typically occur with early pregnancy tests. If you test too early you may not have enough hCG in your urine or blood to indicate pregnancy. It is important to repeat your pregnancy test again a few days later, even if you test negative.

Where to get a pregnancy test

Pregnancy tests are fairly easy to obtain, especially in North America. Home pregnancy tests are available at your local drugstore or pharmacy and at some large department stores. You can also order home pregnancy tests online. Your local sexual health clinic or doctor’s office can also provide you with a urine or blood test.