Imagine heading to the hospital because you think you have a really bad stomachache, only to find out you’re actually in labor. It sounds like something out of a movie, but it can happen. In rare cases, a pregnancy can go unrecognized until the very end — even until labor begins.

Medical researchers use terms like pregnancy denial, cryptic pregnancy or unperceived pregnancy to describe situations in which someone genuinely does not realize they are pregnant. That’s different from a concealed pregnancy, in which someone knows they are pregnant but intentionally keeps it private.

So how does a pregnancy manage to fly under the radar for so long?

When Pregnancy Doesn’t Look Like Pregnancy

For many people, pregnancy comes with some pretty obvious clues: morning sickness, a missed period, weight gain, breast changes and, eventually, a growing belly and fetal movement. But those signs don’t look the same for everyone.

Some people experience few or none of the more recognizable symptoms. Others may have bleeding they mistake for a period, gain little weight or interpret changes in their abdomen as something unrelated to pregnancy. Even fetal movement can sometimes be misunderstood as gas, digestive activity or muscle movement.

And pregnancy denial isn’t necessarily a sign that something is psychologically wrong. Reviews of the research have found cases among people who are otherwise physically and mentally healthy. Some cases do involve underlying psychiatric conditions, but that isn’t true for everyone.

How Rare Is It?

It’s important not to take every surprising pregnancy story online as evidence that this happens all the time. An unrecognized pregnancy is uncommon.

One population-based study published in the British Medical Journal looked at nearly 30,000 births in Berlin and found that about one in 475 pregnancies remained unrecognized after 20 weeks. In about one in 2,455 births, the pregnancy wasn’t recognized until labor.

Those numbers come from a specific German population and shouldn’t be treated as an exact rate for the United States. Still, they show that while rare, pregnancies can occasionally go much further than expected without being recognized.

When Labor Is the First Clue

The most surprising cases are the ones in which someone doesn’t realize they’re pregnant until labor begins. Sudden abdominal or back pain, pressure and contractions can be confusing if pregnancy isn’t even on someone’s radar. And because there may have been little or no prenatal care, there hasn’t been an opportunity for a health care provider to monitor the pregnancy along the way.

That’s one of the biggest medical concerns. Prenatal care isn’t just about seeing the baby on an ultrasound. Regular appointments give providers opportunities to monitor fetal growth, check blood pressure and other aspects of the parent’s health and identify potential complications.

Why It Matters

An unrecognized pregnancy is unusual, but it is a good reminder that our idea of what pregnancy “looks like” isn’t universal. Not everyone experiences the classic symptoms, and the absence of them doesn’t necessarily mean pregnancy is impossible.

For anyone who could become pregnant, unexplained changes in their body — particularly changes in menstrual patterns, nausea, breast changes or abdominal growth — are worth paying attention to. A home pregnancy test or visit with a health care provider can usually help clear up the mystery.

And if someone is experiencing severe abdominal pain, regular contractions, vaginal bleeding or other signs that they could be in labor, they should seek urgent medical care.

Finding out you’re pregnant when you thought you were dealing with a stomachache should certainly be a surprise. But behind the shocking stories is a more important takeaway: Pregnancy doesn’t always follow the script, which is exactly why early recognition and prenatal care matter.