Tested negative 4 days b4 a missed period. the test i took claimed to be only 51% accurate 4 days b4 missed period & 99% after. possible false neg?

About pregnancy test: A urine pregnancy test, done correctly, gives an accurate result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon, and thus lead to a repeat test. If worried, one can repeat a test after another week.