As strange and unlikely as it sounds, as many as one in 600 women will not know that they are pregnant until they are about to give birth or go into labor. This obviously causes some shock for all parties involved, and can also be dangerous for the fetus who is not being considered throughout its gestation. Nonetheless it happens and often results in healthy mother and child. So how is it that some people have long, obvious, and often disruptive pregnancies while others are unaware that they are pregnant at all until their contractions set in?

One reason that this can occur is if the mothers are overweight to begin with. This is not always the case, but it is generally easier to spot a growing baby in the abdomen when someone is thinner. Despite our thoughts that eating for two requires or demands a lot of weight gain, it turns out that it doesn’t. Women who are overweight to obese might be able to put on a mere 11-25 pounds during pregnancy and have a healthy baby. For someone who is already carrying some extra weight, a 15 pound weight gain or so over a few months might not be any reason to cause concerns or suspicions.

There is also something called denied pregnancies, which occurs when the mental or emotional state that a woman is in for some reason leads to her ultimate denial of the pregnancy as it takes place. Some research shows that as many as one in 500 pregnant women are denying the pregnancy to themselves. This might occur if they were emotional scarred at the time the pregnancy occurred, or if they are young and fearful of the consequences. Women can even experience periods throughout pregnancy so if that occurs they might not be as likely to take a pregnancy test even if they suspect it somewhere in their mind.

The actual hormonal changes that occur during pregnancy are different for everyone. While some women might experience tons of morning sickness, other women might not notice any changes to their eating habits or digestive system at all. Because of the wide variety of possibilities, it is possible that some people just don’t experience enough symptoms to notice that are pregnant. People often experience fatigue during pregnancy and things like backaches, but this can also be a sign of normal stress or overworking the body so it is not necessarily an obvious clue.

Another reason that this might occur in slightly older women, is that if they are close enough to the age where they could possibly be going through menopause they might be more likely to assume that than to assume pregnancy. Menopause also causes hormonal disturbances to the body that could be read as similar occurrences. They are also more likely to gain weight unexpectedly and experience fatigue.