Pregnancy tests can give false negative results for women who are actually pregnant when taken five days before a not-yet-missed period. Most home pregnancy tests are designed to be taken three or four days before an expected period, according to Dr. Laurence Cole in Parents.
Parents explains that false positive results, in which a test indicates that a woman is pregnant when she is not, are very rare. Any woman who receives a negative result should try again in a few days. Pregnancy tests also vary in their sensitivity of detecting pregnancy. Using a more sensitive test kit increases the chances of detecting a pregnancy before missing a period.