- Could I have a false positive?
Check out The Truth About False Positives for an in-depth look at false positives.
Essentially, it is possible, but it's unlikely. If you get two lines, you're most likely pregnant. Exceptions: if you have been taking certain fertility meds with hCG, the test may be picking up the hCG from the meds and not an embryo. Also, some tests develop "positive" lines after the time limit. You should NOT read the test after the time limit (usually 10 minutes, but check the directions that came with the test.) Yes, this means you should throw the test away and NOT dig it out of the trash in three hours to see if a line magically appeared. And, if the "positive" line is gray or looks like a "dent" in the test, it is an evaporation line and not a true positive.
Lastly, if you have been pregnant recently, it's possible that the test is detecting residual hCG. However, if a pregnancy ends early on, it's unlikely that hCG will remain in your system very long, so most women have nothing to worry about here. (It's extremely common for women to conceive immediately following an early miscarriage; the body is "primed" for pregnancy, so to speak, and elevated progesterone left from the miscarriage gives the next embryo a great shot at a healthy implantation. So, most women really are detecting a new pregnancy.)
However, the more hCG you had in your system when the pregnancy ended, the longer it will take to dissipate. HPT's can even detect residual hCG for up to 6 weeks following a full-term birth. It's a possibility you should keep in mind if you get positive HPT results soon after a previous pregnancy ended.
Check the HPT Overview page for up-to-date comments on various brands.