The most common reason for a false positive pregnancy test is taking one after a recent miscarriage.

This testing trend has moms-to-be posting side-by-side pics of their tests, looking for reassurance that their pregnancy is progressing.

"It took me about a week to really know that it was true and get the positive blood test back from our doctor. I was just in shock," the reality TV star, 29, recalls.

A 2012 American Society of Anesthesiologists report found that 0.3-1.3% of preoperative pregnancy tests were positive for patients who didn’t know they were pregnant.