Pregnancy is such a routine and frequent fact of life, you’d think we’d know everything there is to know about gestating by now. Yet scientists continue to learn new details about what happens to both mothers and babies in the months leading up to labor and delivery. Here are a few facts that may surprise you.

Stress Without Stressing Out

Despite all the hype about the dangers of a mother’s stress to her fetus, recent research suggests that the opposite might be true. When women experience the normal levels of worry that come from juggling work, life, family and pregnancy, their babies actually get a developmental boost.

In one study, developmental psychologist Janet DiPietro and colleagues found that when mothers reported higher levels of stress and anxiety during pregnancy, their babies were born with faster auditory nerve signals -- a marker of neurological development. It’s still not clear whether a healthy dose of stress is actually good for the baby, or if higher levels of stress go along with other maternal behaviors that boost development. Either way, pregnant women would do well to stop stressing so much about being so stressed out.

“It is a crazy perpetuating cycle,” said DiPietro, of the Johns Hopkins Bloomberg School of Public Health in Baltimore. “The stress field has been oversold and the public thinks stress is really bad for pregnancy, but the data on that are not strong.”

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Pregnant moms get used to frequent pokes, kicks, hiccups and somersaults, but their passengers are a lot more active than they even know. Fetuses move once a minute, on average, DiPietro said. And their movements are remarkably similar to how newborns behave. They yawn, swallow and make breathing motions. They suck their thumbs and play with their umbilical cords and other body parts. Near full-term, fetuses even scrunch and stretch their mouths and noses into the same facial expressions that newborns make.

“Fetuses do the darndest things in utero,” DiPietro said. “While we tend to think of birth as a big transitional period for the fetus and baby, from a developmental perspective, it’s not. There’s nothing new that a newborn does that they’ve learned on the way down the birth canal. They’ve practiced it all before birth.”

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X and Y chromosomes: Some genetic material stays with the mother her entire life.iStockphoto

Despite loads of persistent theories that link the shape of the mother’s belly or the timing of sex during conception to the likelihood that the baby will be a boy or a girl, there is no evidence that any of these old wives’ tales are true, said Emily Oster, an economist at the University of Chicago Booth School of Business and author of "Expecting Better: Why the Conventional Pregnancy Wisdom Is Wrong-and What You Really Need to Know." Studies have also failed to link the fetus’ heart rate to its gender.

But, according to new research, the baby’s gender can affect the health of the mother, DiPietro said. When women carry boys, they are more likely to have trouble remembering things during pregnancy. Giving birth to a boy also raises the risk that the mother will develop an autoimmune disease, possibly triggered by her son’s Y chromosome. Bits of each baby’s genetic material remain in the mother’s body for the rest of her life.


When scientists measure the flow of amniotic fluid near the mouths and noses of third-trimester fetuses, they see patterns that look exactly the same as the patterns of breathing and diaphragm contractions that occur when babies cry.

Crying doesn’t necessarily mean that a fetus is unhappy or in pain, DiPietro said. Doctors consider crying just another normal state of being for newborns and almost-borns. The other states are quiet wakefulness, active wakefulness, deep sleep and sleep that is full of dreams.

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Many women avoid caffeine during their pregnancies, and pregnant women are often greeted with scowls at the espresso bar, but there’s really no need to vilify coffee just because a baby is on board. Many studies show that 200 mg of caffeine -- the amount in two 8-ounce cups of coffee -- is perfectly safe, Oster said. More is probably fine, too.

Caffeine may have unfairly earned its bad reputation from studies that found a rise in miscarriage risk when women drank as many as eight cups of coffee a day during the first trimester, Oster said. But even then, it was never clear that the caffeine actually caused the miscarriages.

The other slightly complicated explanation starts with the known link between nausea early in pregnancy and a lower risk of miscarriage. Morning sickness can also make caffeinated drinks unappealing. So, women who are able to tolerate tons of coffee early in their pregnancies probably have relatively settled tummies -- suggesting that there might be some other reason for the miscarriages besides the coffee.

“All the recommendations say that 200 mg is fine,” Oster said. “You could disagree about more, but a lot of women end up having none. That’s fine unless people are doing it for crazy reasons and say they’re dying for a cup. Some caffeine is definitely fine.”

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Eager to meet their babies and tired of being enormously pregnant, moms try all sorts of tricks to get labor started. Tea, oils, spicy foods, sex: There is no evidence that any of these well-touted strategies work. The only technique proven by research is nipple stimulation, Oster said, but it requires three hours a day, and that can get pretty uncomfortable.

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In the third trimester, fetuses respond quickly with changes to their heart rates, movements and behaviors when their moms are given tasks that either stress or relax them. It goes the other way, too.

Even when a mom doesn’t feel her baby move in the womb, her nervous system gets a small but measurable “jolt,” DiPietro said. “The way I view that is that the fetus is preparing Mom to pay attention to them.”