Taking a pregnancy test can be both exciting and scary, while a false positive can be very confusing. This occurs when the test shows that a woman is pregnant when she is not. A false positive is much more rare than a false negative. It’s a good idea to understand what causes them.
How a Home Pregnancy Test Works
A home pregnancy test uses a bodily fluid, typically urine, to test for a hormone associated with pregnancy. These tests are usually very accurate in checking for human chorionic gonadotropin, or hCG, produced after conception, but errors do occur.
What Usually Causes a False Positive
Most false positives occur because of improper use of the test. An expired test may no longer be accurate, so it is important to check the date on the package before use. Another factor is the recommended length of testing time. If the test is left out past the time it is supposed to be interpreted it may give a positive reading. This often occurs when someone decides to re-check the results. The faint evaporation line that appears on some tests may be mistaken for a positive result. This line is where the results would show a positive, but it is a light gray instead of the color it would be for a true positive.
Other Possible Causes
Certain medications and drugs may have hCG in them or otherwise interfere with the test. During fertility treatments, a woman is sometimes given hCG therapy. If participating in hCG therapy, it is important to ask the doctor how long after a treatment one should wait before a pregnancy test will be accurate. Some medical conditions, such as certain cancers or trophoblastic disease, can cause a false positive. Finally, some women produce low levels of hCG when not pregnant, although this is very rare.
It is possible to get a positive result on a pregnancy test, then have the menstrual cycle proceed as normal with no other signs of pregnancy. This can be the result of a “chemical pregnancy,” when conception occurs but there is an early miscarriage. Chemical pregnancies are somewhat common especially for first-time mothers.
Avoiding or Clarifying a False Positive
Read and follow the directions on the pregnancy test carefully to help avoid a false positive. It is also a good idea to talk with a doctor about whether any current or recent medications could possibly cause this problem. Overall, it is always best to speak with a doctor or wait a couple days and take a second test to confirm a positive result.