We Might Finally Understand What Causes Morning Sickness

The culprit is a hormone called GDF15.

Pregnant woman lying on sofa
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A new baby is often a joyous occasion for parents, but for moms, there’s the dread of morning sickness (also known as hyperemesis), nausea and vomiting that affects up to 70 percent of individuals during the first trimester. In a select few, the unpleasantness doesn’t resolve. Instead, hyperemesis morphs into a far more life-altering condition called hyperemesis gravidarum, where the nausea and vomiting are so debilitating and severe that the condition can result in difficulty eating, extreme weight loss, dehydration, and death in worst-case scenarios.

While treatments are available (but effectiveness may vary), what causes hyperemesis hasn’t been clear — at least until now.

In a study published Wednesday in the journal Nature, an international group of researchers finds the root cause of the condition is a hormone called growth differentiation factor 15, or GDF15 for short. It’s a hormone produced by the placenta — an organ that provides oxygen and nutrients to the fetus and removes wastes — during early pregnancy and acts on the mother’s brain to cause nausea and vomiting. The more sensitive an individual is to GDF15, the sicker they get.

“Hopefully, now that we understand the cause of hyperemesis gravidarum, we’re a step closer to developing effective treatments to stop other mothers going through what I and many other women have experienced,” Marlena Fejzo, a clinical assistant professor of population and public health sciences at the University of Southern California’s Keck School of Medicine who co-authored the study, said in a press release.

In a 2018 paper using data from genetic testing company 23andMe, Fejzo found individuals complaining of hyperemesis were more likely to carry a gene variant for GDF15.

In the new study, the researchers did blood tests on pregnant women, measuring their levels of GDF15 and whether they carried the variant. They found higher levels of the hormone were linked to hyperemesis compared to individuals with no symptoms. Interestingly enough, higher levels of GDF15 — which is produced as well in other tissues and organs like the bladder and kidneys — reduced the risk for hyperemesis for non-pregnancy individuals if they did later get pregnant. Lower levels of the hormone pre-pregnancy due to certain genetic variants increase one’s risk.

The observation led the researchers to test injecting high levels of GDF15 (or a placebo) in non-pregnant mice. After three days, all the mice were given a high dose of GDF15, and found those that were previously exposed to high levels ate normally and experienced less weight loss. The mice who had gotten a placebo experienced the opposite.

These findings give hope that scientists one day will be able to develop a more effective treatment or preventative for hyperemesis

"Knowing this gives us a clue as to how we might prevent this from happening,” Stephen O’Rahilly, director of the University of Cambridge’s Medical Research Council Metabolic Diseases Unit, who led the study, said in the press release. “It also makes us more confident that preventing GDF15 from accessing its highly specific receptor in the mother’s brain will ultimately form the basis for an effective and safe way of treating this disorder.”

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