If it was positive, the test was probably right. That’s because pregnancy tests measure hCG (human chorionic gonadotropin), a hormone that gets into your urine about 6 to 12 days after conception. If you weren’t pregnant, you wouldn’t have hCG in your body at all. So congrats! (Be sure to call your doctor.)
If the test was negative, there’s a chance you could still be pregnant. The biggest factor that could affect your result is when you took the test, since it’s more likely to pick up the hCG in your urine the longer you wait to take it. That’s right: Some tests claim to be 99 percent accurate on the day you miss your period, but that’s probably not true. You’re most likely to get an accurate result if you wait until about a week after you were supposed to start your period.
If it’s been that long, you can trust its accuracy, but if it hasn’t and you got a negative result, be sure to take another test again in a few days.
Plus, more from The Bump:
Source: Your Pregnancy and Childbirth: Month to Month by The American College of Obstetricians and Gynecologists