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New research published by the journal Nature points to the discovery that a single hormone causes nausea and vomiting in pregnancy: GDF15. Researchers found that the amount of this hormone in a pregnant person’s bloodstream before and during pregnancy determines the severity of the nausea and vomiting. GDF15 is released by the body in response to stress, with the receptors of this hormone rooted in the part of the brain responsible for triggering vomiting. 

This information is critical to thinking about treatment for the 2 percent of pregnant people diagnosed with hyperemesis gravidarum, which causes continual nausea and vomiting throughout a person’s pregnancy, well beyond the standard first trimester “morning sickness” experienced by two-thirds of all pregnant people. Hyperemesis gravidarum can cause dangerous weight loss, debilitation, dehydration and a number of other pregnancy complications, some potentially fatal. Awareness of the condition has become more widespread over the past decade, with highly publicized reports of Kate Middleton, the duchess of Cambridge, suffering from it in all three of her pregnancies.

Dr. Marlena Fejzo, a geneticist at the University of Southern California Keck School of Medicine, is the co-author of the new study and for her, this work is deeply personal. When pregnant in 1999, Fejzo suffered from hyperemesis gravidarum — but found her symptoms dismissed by her doctor, who suggested she was merely seeking more attention. She ultimately experienced a miscarriage at 15 weeks following a hospitalization related to her condition. 

Fejzo told The New York Times in a March article that for years she could not find a research mentor for her work on hyperemesis. Much of her early work was done on weekends and evenings, she said. But she persisted. “I would be devastated to see my daughters go through this without having tried everything in my power to make things better,” Fejzo told the Times.

After being denied research funding from the National Institutes of Health (NIH) to further study the genetic components of hyperemesis, Fejzo turned to the private genetic testing company 23andMe, asking them to include a survey question about the condition. The responses 23andMe’s clients sent in helped produce Fejzo’s initial findings, published in 2018, that those with hyperemesis carry a gene variant for the hormone GDF15. 

In their latest paper, Fejzo and her collaborators at the University of Cambridge found that pregnant people with high levels of GDF15 before pregnancy rarely experienced these symptoms. They hypothesize that prolonged exposure to this hormone could result in protecting a pregnant person from experiencing a sharp increase in GDF15 levels that can be triggered by fetal development. 

Clinical trials for medication targeting GDF15 are already underway as part of an effort to reduce nausea and vomiting for cancer patients. This early research published Wednesday suggests that someday, medication could prevent hyperemesis completely if tried before conception — and thus potentially keep parent and baby both safer and healthier. 

A co-author of the study, Stephen O’Rahilly, told Nature that it was possible that GDF15 was just one piece of the puzzle and that other yet-undetermined factors were also at play in hyperemesis gravidarum. 

O’Rahilly, a metabolism researcher at the University of Cambridge, added, “We now have a clear view of what may cause this problem and a route for both treatment and prevention.”   

Flora Peir contributed reporting.