One of the most frequent questions we get here on Sexual Health Connection is from women wanting to know if they are pregnant. I addressed this issue in my last post entitled "Am I Pregnant? How to Know" A variation of this theme are women who have taken a home pregnancy test or even several of them and they turn out negative. The question we then get is: "Can I still be pregnant even though my home pregnancy test is negative?" So for this post I researched into the reasons why these tests can sometimes yield an inaccurate result and how you can up the odds for having more accurate test results.
How do Home Pregnancy Tests Work?
The National Women's Health Information Center tells us that all types of pregnancy tests attempt to detect a hormone called human chorionic gonadotropin or hCG. This "pregnancy hormone" is made when a fertilized egg implants in the uterus. It varies from woman to woman how long this implantation can take. For most women this happens about six days after the egg is fertilized by the sperm but for some women implantation can occur as late as the first day of the missed period. Each day after implantation, the amount of hCG in your system will increase rapidly.
There are two different types of pregnancy tests. One type of pregnancy test is a blood test given by your doctor. A blood test combined with a pelvic exam can be considered the most reliable way to see if you are pregnant. The second type of pregnancy test uses a urine sample and this can be performed at the doctor's office or at home using a home pregnancy test. If you use a home pregnancy test, most commonly you will be instructed to hold a stick in your urine stream where an absorbent strip will collect the urine for testing. Directions are given with each test kit to determine if you are pregnant such as seeing a plus or minus sign and now there are some tests which even show the word "pregnant" in the test results window of the test stick. So it is now easier than ever to test for pregnancy in the privacy and convenience of your own home. But are home pregnancy tests always accurate? It seems the answer depends mostly upon how you use the test.
What types of errors occur with using a Home Pregnancy Test?
There are two ways that a home pregnancy test can be inaccurate. One type of error is to have a false positive reading. This means that although your pregnancy test indicates that you are positive for pregnancy, you are not really pregnant. The other error which can occur is that you get a false negative result. This means that although your test says that you are not pregnant, you really are pregnant.
Why do these errors occur?
Most times when there is an error with home pregnancy tests it is caused by not following the directions given with the test. Bastian et al (1998) found that most false negative results are due to users not using the kits properly. If used correctly most home pregnancy tests have a high degree of reliability although some brands may be more accurate than others.