Women who don't know they're pregnant until they're in labor are sometimes accused of being mentally unstable. It's important to know that some -- not all -- women who experience denied pregnancy have underlying mental health problems that may get in the way of realizing they're pregnant.
Studies examining the mental health of women who didn't know they were pregnant reveal that some have been diagnosed with psychological conditions, including schizophrenia, depression and a range of personality disorders [source: Brezinka et al.]. Other women, meanwhile, felt their confusion was simply due to stress.
Scientists also know that denial, or ruling out pregnancy altogether, can play a significant role in denied pregnancy. Up next: the role of the baby.