Reasons for False Negative Pregnancy Test
A common false negative pregnancy test scenario goes like this. You took a pregnancy test and it came out negative. A few days later your period is late and you take another pregnancy test. It is positive. What happened?
More times than not, when you took your first pregnancy test, you took it a few days too early. Although most tests say that you can test as soon as 5 days before your expected period, this is an AVERAGE statistic that cannot be proven for each and every woman. hCG can show up in the urine as soon as 8 days past ovulation and up to 16 days past ovulation on AVERAGE. Of course, there are specific cases that can be different, depending on when you ovulate. If your ovulation tends to occur on the later end of a normal ovulation period, than your testing window is actually smaller than that of the average. Later ovulation could mean that the only way to get a proper reading is by taking a pregnancy test the day of or after your missed period so that enough hCG is present in your urine to have a proper result. This is the main reason for false negative pregnancy test.
Second reason for false negative pregnancy test is tha not all tests are as hCG sensitive as others. So when taking a pregnancy test earlier than normal you might want to check out the sensitivity (that could be as low as 15 ml/hCG) of the test to make sure you are using something that can detect your hCG levels. You might want to try also taking a few tests if you have a feeling your pregnancy test might be wrong.