When you begin to experience pregnancy symptoms, you will likely want to take a pregnancy test to confirm whether or not you ar pregnant. There are two basic types of pregnancy tests: blood and urine. Home tests are exclusively urine tests, only a doctor can perform a blood test for pregnancy.
How Urine Tests Work
When a fertilized egg implants in the uterine wall, it starts to secrete the pregnancy hormone human chorionic gonadotrophin (HCG). This is why it is recommended that you wait until the first day of your missed period, about two weeks after conception, to take a home pregnancy test.
Urine tests use monoclonal antibodies - manmade molecules used in many laboratory tests – to test for HCG. Home pregnancy sticks have two lines: one is a control line which you will see whether you are pregnant or not, the other line contains the monoclonal antibodies. If there is HCG present in your urine, when it soaks the stick the HCG will react with the monoclonal antibodies, causing a color change that will make the second line appear. Depending on the amount of HCG in the urine, the color of the line will vary in intensity.
How Blood Tests Work
There are two types of blood tests that your doctor can give you:
- Qualitative HCG Test:
This blood test is performed in a laboratory. It only measures the presence or absence of HCG in the blood so it will only give a "yes, you are pregnant" or "no, you are not" answer.
- Quantitative HCG Test
Also performed in a lab, this test, sometimes called the Beta HCG blood test, measures the amount of HCG in the blood. It can detect even low levels of HCG, possibly giving a positive sooner.
Getting Accurate Results
Make sure you read all of the instructions that come with your home pregnancy test carefully. Also, take note of the test reading time given in the test instructions. Certain tests could give a false reading if they’re read too early or too late. A common mistake that women make when reading home pregnancy tests is waiting too long. This could result in a line appearing that could be read as a positive result, but is actually an evaporation line created as the urine on the test dries.
The best time to take a home pregnancy test is in the morning, using your first urine of the day. This urine is less diluted so the HCG levels (if there are any) will be more concentrated. If you have to take a test during the day, try to limit your intake of liquids for a few hours beforehand to minimize the possibility that your urine will be diluted.
Choosing the Best Test for You
There are a few factors to consider when choosing a home pregnancy test:
- Some tests are very sensitive and will detect even very low levels of HCG (12.5 mIU) in your urine. If you want to know as soon as possible, these tests are the best choice for you.
- If you have recently had a miscarriage or recently given birth, you may be prone to false positives. In this case, the best pregnancy test would be one that will only detect a high level of HCG (100 mIU).
- If you’re worried about having trouble reading the test, there are home pregnancy tests available that have digital readouts that simply say "pregnant" or "not pregnant". These tests check for 50 mIU of HCG or higher.
How Common is False Positive?
Home pregnancy tests are about 97% accurate when the results are read on time and all of the instructions are followed correctly. A false positive could be the result of:
- Chemical Interference:
Some drugs contain the pregnancy hormone Human Chorionic Gonadotropin (HCG). If you are taking one of these it can result in a false positive pregnancy test. If you are having infertility treatments and have had a shot of HCG, you should not take a pregnancy test until you are sure the shot is out of your system.
- Chemical Pregnancy:
Unfortunately, a chemical pregnancy is the result of an early miscarriage. Because many pregnancy tests are highly sensitive, they can sometimes detect these pregnancies even though they’ve already ended. When this occurs, the woman will get her period as normal. It is estimated that half of all first pregnancies end in miscarriage.
- Evaporation Lines:
Not technically a false reading, but a result of user error. A common mistake that women make when reading home pregnancy tests is waiting too long. This could result in a line appearing that could be read as a positive result, but is actually an evaporation line created as the urine on the test dries.
If you’ve taken a home pregnancy test and you have doubts about its accuracy, you should see a doctor for a pregnancy blood test. These tests are more sensitive and can give you an accurate reading just one week to 12 days after conception.
See what other women are saying about pregnancy testing in our pregnancy forum.