LOS ANGELES
For decades, women who couldn't stop vomiting during pregnancy were told some version of the same thing: it's normal morning sickness, it's stress, it's anxiety, it's in your head. Some were sent home from emergency rooms still retching. Some lost pregnancies to dehydration and malnutrition before anyone took their symptoms seriously. Dr. Marlena Fejzo, now a geneticist at the Keck School of Medicine of the University of Southern California, was one of them — she lost a baby to hyperemesis gravidarum in 1999, and she has spent the twenty-five years since hunting for the biological proof that the condition sufferers described was never imaginary.
That hunt just produced its biggest payoff yet. In a study published in Nature Genetics, Fejzo and an international team of collaborators analyzed genetic data from nearly half a million women — 10,974 who had experienced hyperemesis gravidarum (HG) and 461,461 who hadn't, spanning European, Asian, African and Latino ancestries — and identified nine new genetic variants linked to the condition. Six of those genes had never before been connected to HG in any research. Combined with earlier discoveries, the total number of confirmed HG risk genes now stands at ten, transforming a condition that was for generations dismissed as psychological into one with a hard, measurable genetic signature.
WHAT HYPEREMESIS GRAVIDARUM ACTUALLY IS
Ordinary morning sickness, unpleasant as it is, affects the majority of pregnant women and typically fades after the first trimester. Hyperemesis gravidarum is a different animal entirely. It affects roughly 2% of pregnancies, and it is defined by nausea and vomiting so relentless and severe that sufferers can become unable to keep down food or even water for days or weeks at a time. Left unmanaged, it can trigger dehydration, malnutrition, rapid weight loss, and electrolyte imbalances serious enough to require hospitalization, IV fluids, and feeding tubes. It's the single most common reason for hospital admission in early pregnancy in many countries, and in extreme cases it can force women to terminate pregnancies they wanted simply because their bodies could no longer survive the illness — or because doctors could not convince insurers or family members that the suffering was real enough to warrant aggressive treatment.
Kate Middleton's very public struggle with hyperemesis gravidarum during multiple pregnancies helped pull the condition into mainstream awareness in recent years, but for most women affected, the condition still comes with an added layer of suffering: not being believed. Patient advocacy groups like the HER Foundation, whose executive director Kimber MacGibbon has co-authored several of Fejzo's papers, have spent years collecting what they describe as heartbreaking accounts of women being told their vomiting was anxiety, an eating disorder, or "just part of pregnancy" — even as they dropped dangerous amounts of weight.
THE GENE THAT CRACKED THE CASE — AND WHAT CAME NEXT
The turning point in HG research arrived in 2023, when Fejzo, working with a University of Cambridge team led by Dr. Stephen O'Rahilly, published landmark findings in Nature identifying GDF15 as a central driver of the condition. GDF15 is a hormone-producing gene that's normally expressed at very low levels outside of pregnancy. When a woman conceives, the placenta begins pumping out GDF15 at levels dramatically higher than baseline — and the new research showed that women who are genetically predisposed to unusually low GDF15 levels before pregnancy become hypersensitive to that sudden hormonal surge once they conceive. Their bodies, in effect, aren't primed for the spike, and the resulting overreaction is severe nausea and vomiting.
"While I have worked, people have continued to contact the HER Foundation with heartbreaking stories like my own, begging for answers," Fejzo said of the years spent chasing the mechanism. "I think we finally have the solution."
That 2023 discovery was a breakthrough, but it explained only part of the picture — plenty of women with severe HG didn't carry the same GDF15 variants, suggesting other genetic pathways were involved. The new Nature Genetics study was designed to answer exactly that question by casting a far wider net. Rather than focusing on a single candidate gene, Fejzo's team ran a genome-wide association study — essentially scanning the entire genetic code of hundreds of thousands of women simultaneously, looking for any variant that showed up more often in women who'd had HG than in those who hadn't.
The result was nine additional genetic regions associated with the condition, several of which point to biological systems that make intuitive sense once you see them: genes involved in appetite regulation, genes tied to nausea signaling pathways, genes connected to metabolism, and genes active in brain regions that govern the body's vomiting reflex. Together, they paint a picture of HG not as a single-hormone problem but as a condition shaped by an interconnected network of appetite, gut, and brain chemistry — much of it overlapping, intriguingly, with pathways also implicated in obesity and metabolic regulation.
WHY THIS MATTERS BEYOND THE LAB
For a condition that has spent decades being minimized, the significance of ten confirmed risk genes goes well beyond scientific bookkeeping. First, it is validation — hard, replicated, multi-ancestry genetic evidence that HG has a real, heritable biological cause, not a psychological one. That matters enormously for patients who have spent pregnancies being doubted by doctors, family members, or their own insurance companies.
Second, and just as important, it opens concrete new avenues for treatment. The GDF15 discovery already reshaped how researchers think about HG drugs — because GDF15 is also a hormone at the center of major weight-loss and metabolic research (some scientists have studied it as a natural appetite-suppressing signal with parallels to how GLP-1 drugs like Ozempic work), the pathway connecting the two conditions gives drugmakers an existing body of pharmacology to build from rather than starting from zero. Clinical researchers are already testing whether medications that blunt GDF15 sensitivity, or that stabilize a pregnant woman's exposure to the hormone before the placenta's surge, could prevent HG in women known to carry high-risk variants. Trials examining other angles, including the anti-diabetic drug metformin as a potential HG risk-reduction tool, are also underway, according to listings on ClinicalTrials.gov.
The newly identified genes tied to nausea and brain signaling could similarly point toward existing anti-nausea drugs, or entirely new ones, that target those specific pathways more precisely than the blunt instruments doctors currently rely on — medications like ondansetron (Zofran) and doxylamine-pyridoxine combinations, which help some patients but leave many others still severely ill.
EXPERT PERSPECTIVE
Researchers involved in the study and outside geneticists who reviewed the findings describe this as a shift from managing HG's symptoms to understanding its root cause. Because the study spanned European, Asian, African and Latino ancestry groups, the findings are also considered more broadly applicable than earlier, narrower genetic studies — a meaningful detail, since research on pregnancy complications has historically underrepresented non-European populations, limiting how well earlier findings translated to all patients.
Fejzo and her collaborators have framed the expanding gene list as proof that hyperemesis gravidarum sits on a biological spectrum, with genetics helping explain why some women sail through pregnancy nausea-free while others end up hospitalized multiple times. That framing matters clinically too: doctors may eventually be able to use genetic risk scores to flag high-risk pregnancies early, before symptoms spiral into medical emergencies, allowing preventive treatment to start earlier rather than playing catch-up once a patient is already dangerously dehydrated.
WHAT THIS MEANS FOR YOU
If you or someone you love has been pregnant and experienced nausea and vomiting severe enough to interfere with eating, drinking, or daily functioning, this research is a reason to push for it to be taken seriously — it is not weakness, anxiety, or an overreaction, and there is now a real genetic basis behind why some pregnancies trigger it and others don't. If HG runs in your family — Fejzo's research has previously shown a strong heritable component, meaning daughters of women who had severe HG face meaningfully elevated risk themselves — it's worth raising that family history proactively with an OB-GYN early in a pregnancy, rather than waiting for symptoms to become an emergency.
For women currently pregnant and struggling, the message from researchers is blunt: severe, persistent vomiting that prevents you from keeping down fluids is a medical condition requiring medical treatment, not something to tough out. Early intervention with IV fluids, anti-nausea medication, and nutritional support can prevent the more dangerous downstream complications, and it is reasonable to seek a second opinion or a maternal-fetal medicine specialist if initial concerns are dismissed.
CONCLUSION
It took a scientist who lived through the worst version of this disease, a quarter century of research, and the genetic data of nearly half a million women to get here — but hyperemesis gravidarum finally has what it never had before: a paper trail written in DNA. Ten genes, a hormone once dismissed as irrelevant, and a research pipeline now aimed squarely at stopping the suffering before it starts. For the women who spent pregnancies being told it was all in their heads, the science has, at last, caught up to what they knew all along.
