20 Surprising (and Horrifying) Facts About Pregnancy

If you don’t know what “lightning crotch” is, buckle up.
Pregnancy is wild.
Pregnancy is wild. / THOM LEACH / SCIENCE PHOTO LIBRARY/Getty Images

The act of bringing another person into the world comes with a whole host of things you might not have anticipated, from a phenomenon called “lightning crotch” and disappearing belly buttons to unexpected excrement and so much more. Read on for surprising, fascinating, and occasionally horrifying facts about pregnancy.

1. People can experience “lightning crotch” during pregnancy ...

People who are pregnant have to deal with a lot of aches and pains, from sore backs to contractions. They also have to deal with something called “lightning crotch”: a sudden, sharp pelvic pain. Lightning crotch doesn’t mean labor has started, and it usually isn’t serious. It’s thought to be caused by the fetus’s position within the parent’s body. As the fetus lowers toward the end of the third trimester, its head puts more pressure on the cervix and the nerves within the uterus. 

2. … and the “ring of fire.”

Lightning crotch is not to be confused with the “ring of fire,” by the way, which is the burning pain some people feel when the baby crowns during birth. 

3. Only 4 percent of babies are born on their due date.

Newborn baby cribs
Newborns in a hospital circa 1960. / H. Armstrong Roberts/GettyImages

The average human pregnancy lasts about 280 days, or 40 weeks. Doctors calculate how far along a pregnancy is based on the first date of the person’s last menstrual period. So saying someone is 30 weeks pregnant means it’s been 30 weeks since they started their last period, not since they conceived. 

The idea that a baby will make their grand arrival sometime within the 40th week isn’t very accurate. In the 19th century, an obstetrician named Frederich Naegele came up with a formula to calculate a person’s estimated due date based on their menstrual cycle. It’s fairly simple: Just go back three months from the date of their last menstrual period, then add one year and seven days. This puts their due date about 40 weeks from their last period. But was there a big flaw in his logic: Naegele’s rule assumes ovulation on the 14th day of a regular, 28-day menstrual cycle. Most menstrual cycles, however, range between 23 to 35 days. And even if someone does get their period every 28 days on the dot, when they actually ovulate within that cycle can still vary a bit. 

Still, that doesn’t mean that due dates are meaningless—over 90 percent of babies are born within two weeks of their estimated due dates.

3. It’s possible for someone to get pregnant in their forties, fifties, and beyond.

People who ovulate tend to be most fertile between their late teens and late twenties, and their fertility is typically still fairly good in their early thirties. Risks do increase for people over 35 years old, and though pregnant people who are 35 years or older are considered to be of “advanced maternal age” (which used to be referred to as “geriatric pregnancy”), that doesn’t mean getting pregnant in your late thirties or even forties is impossible. 

4. One woman gave birth when she was 59 years old.

In 1997, a British woman named Dawn Brooke set a world record when she gave birth at 59 years old. She holds the record for the oldest known person to have gotten pregnant without medical intervention (though she was on hormone replacement therapy at the time). 

5. Another used IVF to have a baby when she was 74. 

Brooke isn’t the oldest known person to have ever given birth: In 2019, a woman made headlines when she gave birth at age 74 after getting pregnant via in vitro fertilization. 

6. A woman was pregnant with nine fetuses.

In May 2021, a woman named Halima Cisse welcomed nine babies into the world. For most of her pregnancy, she was totally unaware that she was carrying nonuplets. Doctors initially thought Cisse was carrying seven fetuses. But after going to a specialist clinic in March of 2021, doctors discovered two other fetuses within her womb. Cisse delivered all nine babies via C-section when she was 30 weeks pregnant. Amazingly, every single one of them survived. The nonuplets—four boys and five girls—remained in Morocco for 19 months before finally heading home to Mali.

7. The belly button can change shape when you’re pregnant.

Cropped shot of a woman holding her pregnancy belly
Sometimes innie belly buttons become outies during pregnancy. / LumiNola/E+/Getty Images

As the fetus grows, it causes a person’s abdominal muscles to stretch. That stretching can eventually cause their belly button to “pop” or become so stretched out that it seems to just disappear entirely. Going from an innie to an outie usually doesn’t hurt, though some people suffer from mild irritation when their new outie belly buttons start rubbing against their clothing. A person’s belly button will typically go back to normal once they’re a few months postpartum.

8. Some people develop a dark line on their stomach while pregnant.

In addition to a brand new outie belly button, some people will also notice a dark stripe stretching vertically across their abdomen. It’s called the linea nigra, or “black line.” Everyone has a linea alba, a strip of connective tissue that runs between the left and right side of the rectus abdominis. The linea alba is particularly visible on people with a shredded six-pack—it’s what causes the groove between the two sides of their abs. When a person gets pregnant, hormone shifts cause the connective tissue to darken and become the linea nigra.

9. Morning sickness doesn’t just happen in the morning.

Morning sickness—the nausea and vomiting some people experience during pregnancy—is a misnomer. It can actually last all day. It’s believed 70 percent of people who are pregnant suffer from the condition. Morning sickness usually starts within the first month, and lasts throughout the first trimester, though some people will experience it throughout their entire pregnancy. Doctors still don’t know what exactly causes it. Recent research has pointed toward a hormone called GDF15, which according to New Scientist may have “evolved to trigger food aversion in response to, say, poisoning.” Morning sickness, though annoying, is supposed to be fairly mild; people who suffer from extreme vomiting and nausea are usually diagnosed with a condition called hyperemesis gravidarum, which Kate Middleton, the Princess of Wales, had during her three pregnancies.

10. You grow a whole new organ when you’re pregnant.

Pregnant people aren’t just growing a fetus—they’re also growing an entirely new organ. Like the fetus, the placenta also grows inside the uterus; it was long referred to simply as “afterbirth,” as it’s delivered after the baby is born. But the organ is crucial during pregnancy. Twenty percent of a pregnant person’s blood goes through the placenta to the fetus. The placenta is how the fetus gets nutrients and oxygen, and also how waste is removed from its blood. It’s no small organ, either: By the time a baby is born, the average placenta is about 10 inches long and 1 inch thick. 

11. Some people eat their placentas after pregnancy.

Some people even eat their placentas for the organ’s supposed health benefits, such as its alleged ability to increase energy and milk supply, though there’s no concrete scientific evidence to back up those claims. Experts at the Mayo Clinic warn against consuming the placenta, citing the risk of bacterial infections.

12. By the end of pregnancy, the uterus weighs about 2 pounds.

Illustration of a uterus
The uterus goes from the size of a lemon to 2 pounds during pregnancy. / Maryna Terletska/Moment/Getty Images

An average, non-pregnant uterus is often compared to the size of a lemon. But by the time a baby’s due, it will grow to be roughly the size of a watermelon and weigh about 2 pounds. 

13. The internal organs rearrange during pregnancy.

All that growth requires some serious internal rearrangements. A pregnant person’s uterus pushes downward onto the bladder, making them have to pee more often. It also pushes upward to smush the stomach and intestines, which can cause heartburn and make it hard to eat a lot of food at once. The way it squishes a person’s lungs in the final trimester can also cause them to feel out of breath. Fortunately, all those organs will typically return to their proper places within a few months of the baby’s birth. 

14. Pregnancy can cause the pelvis to separate.

When a person is pregnant, their body releases a lot of a hormone called relaxin, which causes their joints and ligaments to loosen and shift in preparation for labor. But sometimes, that loosening goes a bit too far. Some pregnant people suffer from symphysis pubis dysfunction, which means their pubic symphysis—the joint between a person’s left and right pelvic bones—has separated. Though the condition isn’t dangerous, it can be incredibly painful. 

15. Pregnancy changes the brain ...

illustration of the brain
Pregnancy literally changes the brain. / MirageC/Moment/Getty Images

Speaking of changing organs, pregnancy also alters a person’s brain. The gray matter—that is, the tissue that’s crucial for day-to-day function—shrinks in the areas of the brain that are responsible for responding to social signals. According to a 2016 study, it’s believed this may make the parts of a pregnant person’s brain that handle responding to their baby’s needs work more efficiently. It allows their brain to become more specialized. Those brain changes aren’t as short-lived as other pregnancy symptoms: They were shown to last for at least two years.

16. … and other parts of the body.

It isn’t the only potentially permanent changes a person may encounter: All those hormones can make some people’s hair change texture and go from straight to curly or vice versa. And some people will wind up with an entirely new shoe size, thanks to the way pregnancy can cause their feet to flatten and widen.

17. Fetal cells become part of the parent.

Sure, a pregnancy only lasts nine months—but tiny parts of the fetus will stay with the pregnant parent forever: They become what some have dubbed “genetic chimeras.” Fetal cells escape from the placenta and enter their body, where they linger for a long time. They circulate throughout the birthing parent’s body and can even embed in their tissues and organs.

18. Fetal cells can be harmful—but they might also be helpful.

Those wayward fetal cells can cause problems—they’ve been associated with issues like autoimmune diseases and preeclampsia, a potentially life-threatening blood pressure problem that can develop during pregnancy. But the fetal cells may also be helpful. It’s thought they may be able to protect against breast cancer and heart attacks and heal wounds (though much of the evidence is both lacking and inconsistent).

19. A pregnant person’s body knows the fetus isn’t foreign tissue.

The human body will often try to reject foreign tissue, which is why transplant patients are given medication to prevent their immune system from attacking their new organ. The body will produce chemokines, which recruit immune cells to go on the attack. That doesn’t happen with a pregnancy, though: Instead, once the embryo implants in a person’s uterus, it turns off the genes inside the decidua—the mucus membrane that lines the uterus—that would ordinarily trigger a person’s immune system to attack the new, foreign object. 

20. It’s common to poop (and pee) during labor.

Here’s a fun detail you probably won’t hear many people mention when recalling their birth experiences: Shit happens … literally. Many people poop during labor

It makes sense that it would occur: the muscles people use during a bowel movement are the same ones they use while pushing during labor. The baby’s position can also determine whether a person will poop or not. If the baby is face-up instead of face-down in the birth canal, their body pushes more against their parent’s intestines, likely stimulating a bowel movement. 

Pooping during labor seems embarrassing and generally unpleasant, but it’s thought to help the newborn by upping the amount of fecal bacteria that the baby comes into contact with. This little taste of their parent’s fecal microbes can improve the baby’s gut microbiome. Those born via C-section aren’t exposed to the blend of microbes hanging around the parent’s perineum, which is thought to put them at higher risk for immune-related disorders later in life. In one 2020 study, researchers actually suggested mixing a bit of the birthing parent’s fecal matter into breast milk to help boost a C-section newborn’s gut microbiome—though they caution not to do this at home because you can easily start exposing the baby to dangerous bacteria.

If a person is hooked up to an IV for fluids while in labor, they’ll probably pee a lot too. And if a person has had an epidural and can’t pee on their own, a nurse will likely have to empty their bladder with a catheter, as a full bladder could block the baby’s progress through the birth canal. 

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This story was adapted from an episode of The List Show on YouTube. Subscribe to Mental Floss for new videos every week.