When you think you might be pregnant, every minute you have to wait to find out can seem like hours. A little impatience can lead to several test errors. Home pregnancy tests first developed in the 1970s allowed you to test for the early pregnancy indicator–the human Chorionic Gonadotropin (hCG)–in your urine. The tests are accurate when you follow all the instructions carefully. Mistakes in taking the test or interpreting the results account for the majority of false positive or negative results. When you take the test is as important as how you take it.

User Error

Home pregnancy tests are easy to use, but skipping certain steps or ignoring a few simple instructions can affect its accuracy. Expose the test to urine for the recommended time period. Handle the strip correctly during and after testing. Lay the test strip or wand flat for the waiting period required in the instruction pamphlet. That means no rotating it or tilting it to peek–even though those few minutes seem like hours. When the time is up, read the results. A positive result is what your instructions specify. You’ll see a cross, a plus sign, or a “yes” clearly showing in your test window. If the control window indicates the test has worked, trust the result.

Don’t squint and hold the test up to the light or scan it on the computer (yes, some women have done this) to enlarge the results on the screen, or keep it in your nightstand to check and recheck it for the next 48 hours. Any faint lines you see after this much time has elapsed are likely evaporation lines. If your instructions say that the test readings are invalid after 10 minutes, don’t look at the result after 10 minutes. Put the test down. Go have a cup of herbal tea.

Timing

One first indicator of pregnancy is the presence of hCG (human Chorionic Gonadotropin) in a woman’s blood or urine. The hCG increases rapidly in early pregnancy and continues to increase until about eight weeks into the pregnancy. If you test too early in a pregnancy, your test might not pick up on very low levels of the hormone. Women have different levels of hCG early in their pregnancy, so if you think you are pregnant and get a negative result, wait a few days and test again. Maybe you miscalculated your menstrual cycle. Keep a record of your menses to avoid testing when your period is not due.

Try and take your home test in the morning. Drinking lots of liquids dilutes the concentration of existing hCG levels in the urine and can affect the ability of your home pregnancy test to detect it.

Medications or Conditions

Certain medications that contain hCG, such as Pergonal and Pregnyl, can affect the results of your home pregnancy test. Rare medical conditions may also alter the accuracy of the results. Check with your doctor for more information.