Did you read and follow all of the directions on the test, and check the results within the recommended time frame? And did the results look like the instructions said they would? If so — congrats! — chances are very, very slim that you aren't pregnant.
That's not to say it doesn't happen. If you miscarried or had an abortion in the past 8 weeks, have received a fertility drug that contains hCG, or have a tumor that secretes hCG, then the hormone could show up in your pee without you being pregnant. It's also not totally unheard of for a test to be defective or to give false results past its expiration date. (Take two different brands of tests if you're suspicious about your results.)
If you are testing early (especially if it's before you've had time to miss a period), there's also the possibility that the fertilized egg could implant, grow big enough to put hCG in your system, and then simply stop developing (usually because something's wrong with its chromosomes). This is called a "chemical pregnancy” and is actually super-common (it happens to over 30 percent of all fertilized eggs), but most women don't even notice. If this happened, you'd still get your period as usual (well, maybe a little bit heavier and a day or two later).
It's also possible you're seeing what's known in mom circles as an "evaporation line.” Yeah, it had to get more complicated. Basically, this is when you look close and see the strip of stuff on the test that is meant to turn a color (usually pink or blue) when hCG is detected. But instead of some pretty pink or blue, you see a grayish line or what looks like a dent where the line should be. Here's the deal: If the line doesn't turn the exact color mentioned in the instructions (yes, again with the instructions — it never stops!), it's not positive. Similarly, if a line — of any hue — pops up after the time period specified (usually 10 minutes), it doesn't count either. Sorry for the letdown.
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