Though I only have three children, I've taken dozens of pregnancy tests over the years. At various points in my life I've been worried about false positives, false negatives, faulty tests, tests read too early, tests read too late, and tests that I was sure that I had simply read wrong. Most of my concerns were unfounded—I was pregnant when the test said I was, not pregnant when it said I wasn't, and never had a faulty or misread test in all the pregnancy tests that I took.
However, over the years I did learn several little known facts about pregnancy tests that might have eliminated many of my worries.
False positives are extremely rare.
A pregnancy test that says you are pregnant when you are not (a false positive) is incredibly rare. Most women that I know and doctor's offices that I've asked have said that a positive is a positive is a positive.
False negatives are more common than false positives.
A pregnancy test that says you are negative when you actually are pregnant (a false negative) is more common than a false positive. According to WebMD, these often occur when you didn't ovulate when you expected, miscounted your cycle, or tested too early.
The earlier you take a test, the more likely you are to get a false negative.
Many pregnancy test boxes show that the test may be taken a certain number of days earlier than the date that you expect your period. However, the earlier you test, the more likely you are to receive a false negative. If you read the insert in the packaging, you'll find that a smaller percentage of women may get a positive 4 or 5 days before they expect their period. That number grows the closer you get to the date of your expected period.
Chugging water before taking a pregnancy test may impact your results.
Guzzling water will dilute your urine and make your result more difficult to read. This is especially true when you are testing several days before your period is due. For the most accurate and readable pregnancy test results, wait until morning or until you naturally have to go during the day.
Digital results don't show up forever.
With my oldest daughter, I used a regular plus or minus pregnancy test and took a picture of the stick for her baby book. With my middle child I thought it would be cute to do a digital test where the "Pregnant!" result shows up. However, I didn't take the picture right away, and after time, the result will disappear. Don't be surprised when this happens to your digital pregnancy test.
WebMD: When to take pregnancy tests; http://www.webmd.com/baby/guide/pregnancy-tests?page=2
EPT; Test Accurately; http://www.testaccurately.com/index.html