Why some women don't know they're pregnant until labor

Now, this kind of pregnancy actually isn't that uncommon. A 2011 British study found about one in every 2,500 pregnancies is unknown until labor begins.

It even happens often enough that TLC was able to make a show about it. 

"I think I just had a baby."

These kind of pregnancies — when mothers are unaware that they are pregnant — are called cryptic pregnancies and doctors say certain women are more likely to have them than others.

PregnancyCorner explains women who have irregular menstrual cycles or women who are obese may be less likely to realize they are pregnant.

There are also psychological factors that can lead to cryptic pregnancies.

Psychology Today says a woman experiencing a lot of stress could cause the fetus to produce low levels of the hormone HCG, which would cause milder, potentially unnoticeable pregnancy symptoms.

Low levels of HCG can even cause a pregnancy test to be negative when the woman is in fact pregnant.

The Centers for Disease Control and Prevention recommends that all women of reproductive age take steps to keep their bodies healthy and visit their doctors regularly in case they become pregnant.