Baby Hopes explains that an invalid positive pregnancy test can occur because of a chemical pregnancy, an evaporation line on the test, chemical interference or a missed reaction time. Baby Hopes says that approximately one out of four pregnancy tests that claim to be positive end in a chemical pregnancy.Continue Reading
According to Baby Hopes a chemical pregnancy is an early miscarriage that occurs shortly after implantation. Due to early pregnancy tests, a woman can see a positive test result although the pregnancy does not last.
Missed reaction time, according to Baby Hopes, means that a woman read the test result after the recommended time. Tests can become invalid after a specific time stated in the instructions because additional lines sometimes show up. These extra lines do not indicate a positive test.
Those who use hCG, also known as Human Chorionic Gonadotropin fertility treatment, must wait until the shot has had enough time to metabolize. If a woman takes a pregnancy test before the recommended waiting period, the test is considered invalid: It can give a false positive result, according to Baby Hopes.
As urine passes over the test strip, sometimes an evaporation line appears. This extra line is often misinterpreted as a positive result. Baby Hopes explains that an easy way to determine if this line is an evaporation line is to see if the line is a different color than the test instructions state.
WebMD states that sometimes a false negative result occurs when a woman takes a test too soon before her missed menstrual period. A false negative may result if the test is expired, the woman took the test incorrectly, the woman's medications interfere with the test or the urine sample is too diluted.Learn more about Pregnancy