Pregnancy Test

How Does a Pregnancy Test Work?

Even the most uncomplicated pregnancy will involve a number of tests, from the initial pregnancy test to screenings for disease to others that mean little to you, but a great deal to your medical practitioner.

Every pregnancy test, whether urine or blood, works by detecting the presence of human Chorionic Gonadotropin (hCG). If done correctly, a home pregnancy test will be almost as accurate as one done in a lab or doctor's office, but with more privacy and a lot less waiting. They are easy to use and relatively inexpensive. The sooner you know you're pregnant, the sooner you can start taking the best possible care of yourself and your baby. However if done too soon or incorrectly, you could get a false negative result which might cause you to postpone seeing your medical practitioner and taking care of yourself. Even a positive answer can be a problem if you assume that there's no need to see the doctor now that you have the answer. Home tests are a great first step but should never replace a visit to your practitioner.

A pregnancy test done in a lab or doctor's office will usually use urine. Some practitioners prefer blood tests, which are more accurate and can help date the pregnancy by measuring the exact amount of hCG in the blood (important if you have irregular periods of if an ectopic pregnancy is suspected). A blood test can detect hCG earlier than a urine test, about a week after conception. Lab and office tests aren't as convenient as those done in the home, but their increased accuracy can give you faith in the results.

Your blood will be tested for type (A, B, AB, or O) and antibody (Rh negative or Rh positive). If your blood is Rh negative and your baby's blood is positive, your pregnancy will require some special care. Another blood pregnancy test will check for anemia, while others will check for syphilis, HIV, hepatitis B, and whether or not you are immune to rubella.

You may have another pregnancy test about four months into your pregnancy to check for alpha-fetoprotein (AFP), which can signal a risk of neural tube defects (spina bifida) or Down Syndrome. Other tests you may have include amniocentesis, chorionic villus sampling (CVS), and genetic testing - all designed to catch a possible problem early, offering time to prepare and possibly begin treatment while still pregnant.