Does Morning Sickness Make Your Baby Smarter?

A recent headline promised, "Women Who Suffer From Morning Sickness Are More Likely to Have Babies With High IQ [2]." This is great news, right? If you're going to spend weeks or months nauseous and throwing up, it helps to know your suffering is making your kid smarter. But what if you go through pregnancy without throwing up? Depending on which study you read, 10 percent to 50 percent of women don't get morning sickness (a slightly baffling range). Does that make their kids dumber?

Of course not. The headlines oversimplified a new Journal of Pediatrics study [3] that—at this point—hasn't proven anything per se about the impact of morning sickness on IQ. Such has been the case with many morning sickness headlines over the years. A few examples: "Morning Sickness Vomiting Risks Birth Defects [4]" and "Morning Sickness Lowers Risk of Breast Cancer [5]."

Though the first case of morning sickness was documented in 2000 B.C., scientists still don't know exactly why it happens or how it works (or, for that matter, why it's called morning sickness, since it happens any time of day and is a normal part of pregnancy, not a sickness). According to biologist Samuel Flaxman, who studies the phenomenon from an evolutionary perspective, morning sickness was ignored well into the 20th century because it was believed to be a psychological problem that didn't warrant study.

About 1 percent of morning sickness cases are an extreme form called hyperemesis gravidarum [6], which causes relentless vomiting, weight loss, and dehydration and can require hospitalization. The vast majority of cases aren't dangerous, but they still have obvious downsides-physical and economic costs. (One study [7] found that women lose nearly 14.5 million hours of work each year to morning sickness.) But there is one real upside: The sicker a woman is during pregnancy, the less likely she is to miscarry. This doesn't mean women without morning sickness are likely to miscarry. They deliver fine 90 percent of the time. But it does mean that morning sickness is associated with healthy pregnancies

There is extensive scientific debate over why morning sickness exists. Some believe it's simply a side effect of the hormonal change that comes with being pregnant, but several studies [8] indicate that morning sickness evolved as a way to protect embryos. Flaxman has found that nausea and vomiting in pregnancy are triggered by foods that posed the greatest risk to our ancestors' fetuses, including meats (which could contain dangerous bacteria, fungi, or viruses) and strong-tasting vegetables (which often get their taste and odors from natural chemicals that are toxic in large amounts).

The results of the recent Journal of Pediatrics study might provide another piece of evidence in favor of the "embryo protection" argument. But it might not. The point of that study was actually to look at the long-term safety of Diclectin, the most common morning sickness drug used today. And it found that the drug Diclectin was safe. (It was funded in part by the company that makes Diclectin, which the study's co-author is a paid consultant for.)

As part of determining the safety of the drug, the researchers checked the IQs of children born to women with and without morning sickness. And they did find that children born to mothers with morning sickness were more likely to have a higher IQ. A few caveats, however: Each child in the study had a normal IQ, and some children in each group had IQs that were a bit higher than normal. The difference was that a few more of those kids with higher IQs were born to mothers who'd had morning sickness than to those who hadn't. That increase in IQ was detectable through an IQ test, but it wasn't a child-genius level change—it was so slight, a teacher probably wouldn't be able to detect it in a classroom.

More research would be needed to determine what the slight IQ difference means and whether it was truly due to morning sickness. This study was small and had far more children born to mothers with morning sickness than without (92 versus 29). It relied on self-reported data, which meant that instead of objectively measuring the women's hormone levels or their symptoms, the researchers asked the women to report their experiences, then ranked their morning sickness based on those reports. Some of this was information gathered after the pregnancy ended. Because this method is subjective, it's often questioned, particularly when studying pregnancy. It's well-known that women block out and alter memories relating to childbirth. (Why else would we want to subject ourselves to it more than once?) Gideon Koren of the Hospital for Sick Children in Toronto, one of the IQ study's authors, actually wrote a paper in 2004 [9] illustrating that self-reported data on morning sickness introduce bias into studies.

But at this point, it's difficult to study pregnancy any other way. From the 1930s to the 1950s, researchers studied morning sickness by X-raying pregnant women while they ate and even while they gave birth. Obviously, no one wants scientists doing that today.

The important thing to remember about morning sickness is this: in its most common form, all evidence indicates it's harmless, even good. But it's also not a sign of trouble if you don't have it. In fact, worrying about morning sickness one way or the other is the only real risk here—one thing we know is that stress is bad for a fetus [10].

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