Pregnancy in most moms-to-be is unmistakable — you gain weight, your baby bump grows, you experience symptoms (from morning sickness and fatigue to backache and edema), and you feel those adorable little kicks.

But in some women, expecting a baby goes unnoticed in a phenomenon known as a cryptic pregnancy. Here’s how it’s possible to not know you’re pregnant.

What is a cryptic pregnancy?

A cryptic pregnancy — also known as a “stealth pregnancy” or a “denied pregnancy” — is when a woman is pregnant but doesn’t know it (or denies it) up until labor begins.

How does a cryptic pregnancy happen?

It sounds implausible, but cryptic pregnancies happen more often than you’d think, occurring in about 1 in every 475 pregnancies.

Women with cryptic pregnancies often don’t have the typical pregnancy symptoms that most moms-to-be have. And if they do have them, they don't realize what they are.

Women who have cryptic pregnancies frequently don’t have or don’t notice morning sickness, they don’t have or don’t notice abdominal swelling, they either don’t gain weight or don’t register their weight gain as anything out of the ordinary.

They also don’t find the absence of their periods odd, perhaps because they normally have irregular periods or because they've taken birth control pills or shots that have made their periods sporadic or non-existent.

And they don’t notice fetal movement — or if they do, they chalk it up to gas or general stomach upset.

Who is more likely to have a cryptic pregnancy?

Cryptic pregnancies tend to be more common in the following circumstances:

  • In women who are obese. That’s not to say it can’t happen in women of average weight, just that obese women would be less likely to notice the physical changes and abdominal growth that occurs during a pregnancy. Cryptic pregnancies may also happen in thinner women, especially if they're tall, because they may be carrying their babies differently.
  • In women with irregular periods, since they wouldn’t think it's out of the ordinary that they’re missing their periods for months at a time.
  • In some very athletic women, who may already have irregular periods and may not realize they’re pregnant since their tight abdominal muscles could hide a baby bump well.
  • In women who get pregnant soon after giving birth, since they're not expecting their period to return yet anyway and might assume that any weight gain and abdominal swelling are from the previous pregnancy.

What are the symptoms of a cryptic pregnancy?

Symptoms of a cryptic pregnancy are the same as those of a regular pregnancy. The only difference: The mom-to-be may not recognize those symptoms as being related to pregnancy.

She may feel very tired, but believe because it’s because she’s overworked or not getting enough sleep. She may experience nausea, but think it's because of something she’s eaten.

She may also attribute her absent periods to her birth control, perimenopause or her usual irregular-period pattern. Or she may think that any spotting she’s noticed, which is normal for a lot of expectant moms, is her period.

Is a cryptic pregnancy dangerous for the baby or the mother?

Part of what helps make a pregnancy healthy is getting excellent prenatal care.

When a woman doesn’t realize she’s pregnant, she isn’t able to get the prenatal care she needs, she may not eat as well as she should for a healthy pregnancy and baby, and she may engage in lifestyle habits that aren't safe for a growing fetus (drinking alcohol, for instance, or smoking). 

What’s more, she may not even realize she’s in labor when it begins, and that could lead to an unattended birth.

Babies born to moms who didn’t realize they were pregnant are often born at low birthweights or prematurely. Also, because it’s impossible to date a cryptic pregnancy, the baby’s gestational age at delivery and whether extra monitoring or treatment would be required after birth may not be clear.

Does a baby born after a cryptic pregnancy need special treatment?

After birth, the baby will need to be assessed by a doctor to figure out whether he needs any special treatment. This will be determined by examining the baby’s condition, size and Apgar score, among other measures of newborn wellbeing.

While moms-to-be who don’t realize they’re pregnant can have healthy babies, it’s always better to get excellent prenatal care to minimize the risks and increase the chances that the baby will be healthy. If you notice any unusual symptoms, weight gain or period changes, give your doctor a call.