Hyperemesis gravidarum (HG) is a severe form of pregnancy-related nausea and vomiting that goes far beyond typical morning sickness. It affects roughly 2 to 3% of pregnancies and is defined by persistent vomiting, weight loss of 5% or more of pre-pregnancy body weight, and dehydration that makes it impossible to keep down enough food or fluids. It is one of the leading causes of hospitalization in early pregnancy.
How It Differs From Morning Sickness
Up to 80% of pregnant people experience some nausea during the first trimester, and for most, symptoms are manageable. With HG, the vomiting is relentless, often exceeding three or more episodes per day, and it doesn’t respond to simple dietary changes or rest. The distinction isn’t just about frequency. Women with ordinary morning sickness typically have normal vital signs and a normal physical exam. Women with HG show signs of dehydration: dry mouth, rapid heart rate, poor skin elasticity, and drops in blood pressure when standing up.
The functional toll is just as telling. HG severely impairs the ability to perform daily activities, from working to caring for other children. Fatigue, constipation, and an inability to tolerate any oral intake are hallmarks. When the body can’t get enough calories, it begins breaking down fat for energy, which produces ketones detectable in urine. Ketones in the urine aren’t diagnostic on their own, but they serve as a useful marker of how starved the body has become.
What Causes It
For decades, the cause of HG was poorly understood, and women were sometimes told their symptoms were psychological. That picture has changed substantially. A 2023 study published in Nature identified a hormone called GDF15 as a central driver. During pregnancy, the fetus and placenta produce large quantities of GDF15, which acts on a specific area of the brainstem that controls nausea and appetite. The vast majority of GDF15 circulating in a pregnant woman’s blood is of fetal origin.
The key insight is that it’s not just how much GDF15 the fetus produces, but how sensitive the mother’s body is to it. Women who have naturally low levels of GDF15 before pregnancy appear to be more vulnerable, because their brainstem receptors haven’t been “desensitized” to the hormone. When fetal GDF15 surges in early pregnancy, the response is overwhelming nausea. Conversely, women with beta-thalassemia, a blood condition that causes chronically high GDF15 levels, report very low rates of pregnancy nausea. In animal studies, prior exposure to GDF15 reduced the intensity of the nausea response, confirming this desensitization effect.
Typical Timeline
HG usually begins early, around 4 to 5 weeks of gestation, before many people even confirm their pregnancy. Symptoms tend to peak between 10 and 16 weeks. For most women, nausea and vomiting of pregnancy resolves by 16 to 20 weeks, though HG can linger longer and a small percentage of women experience symptoms throughout the entire pregnancy.
In a longitudinal study tracking women admitted to the hospital with HG, 100% reported nausea and vomiting at the time of admission. By the end of pregnancy, those numbers had dropped to about 16% for nausea and 10% for vomiting. Anxiety, which affected 69% of women at admission, fell to 19% by late pregnancy. By the third trimester, psychological stress levels in women recovering from HG were actually lower than in a control group of women who hadn’t experienced severe vomiting.
Risks to the Mother
The most common complications are dehydration and nutrient deficiencies, which are addressed with intravenous fluids and electrolyte replacement during hospital visits. Severe, repeated vomiting can also cause tears in the lining of the esophagus (known as Mallory-Weiss tears) and, rarely, gastrointestinal bleeding.
The most dangerous complication, though uncommon, is a brain condition caused by severe vitamin B1 (thiamine) deficiency. Prolonged malnutrition depletes thiamine stores, which can lead to confusion, difficulty with eye movements, and loss of coordination. If not caught quickly and treated with thiamine replacement, it can progress to permanent memory loss. This is why healthcare providers monitor nutritional status closely in anyone with prolonged HG.
Risks to the Baby
For most pregnancies affected by HG, the baby does well, especially when the mother receives adequate treatment. However, a large meta-analysis combining data from millions of pregnancies found some measurable risks. HG was associated with nearly three times the odds of very preterm birth (before 34 weeks) and a 43% increase in the odds of very low birth weight (under 1,500 grams). Babies born to mothers with HG were also somewhat more likely to need neonatal intensive care admission.
Interestingly, the same analysis found that HG pregnancies had lower rates of both stillbirth and very large babies (over 4,000 grams). The takeaway is that while HG does carry some fetal risks tied to maternal undernutrition and low weight gain, the most severe outcomes are associated with poorly managed or untreated cases.
How It’s Managed
Treatment focuses on two goals: controlling the nausea and replacing what the body has lost. For many women, this means one or more visits to a hospital or infusion center for intravenous fluids to restore hydration and correct electrolyte imbalances. Potassium and thiamine are among the nutrients most commonly depleted and supplemented.
Anti-nausea medications are a mainstay of treatment and are typically tried in a stepwise fashion, starting with milder options and escalating if symptoms don’t improve. Some women manage HG at home with oral medications and dietary modifications (small, frequent, bland meals), while others require repeated IV hydration or even a feeding tube in the most refractory cases. The experience varies widely, and treatment is often adjusted week to week as symptoms fluctuate.
Hospitalization is generally reserved for women who cannot keep down any fluids, are losing weight rapidly, or show signs of complications. Most hospital stays are short, focused on rehydration and symptom stabilization, but some women are readmitted multiple times throughout the first and second trimesters.
Recurrence in Future Pregnancies
One of the most common questions women with HG ask is whether it will happen again. The answer, unfortunately, is that recurrence is likely. A population-based study of nearly 4,800 women with HG in their first pregnancy found that 15% had a recurrence in their second pregnancy using strict diagnostic criteria (ketones in urine and more than 5% weight loss). But survey-based research paints a more sobering picture: among women who self-reported their experiences, 81% described severe nausea and vomiting in their next pregnancy.
The gap between those numbers likely reflects differences in how recurrence is defined and measured. Many women experience significant symptoms that don’t quite meet the clinical threshold for a formal HG diagnosis but are still debilitating. The biological mechanism supports the pattern: if a woman’s sensitivity to fetal GDF15 is partly determined by her own baseline hormone levels, that sensitivity is unlikely to change between pregnancies. For women planning a future pregnancy after HG, discussing a proactive symptom management plan before conception can help reduce the severity of early symptoms.
The Psychological Toll
HG is isolating in ways that are hard to appreciate from the outside. At the time of hospital admission, roughly 69% of women with HG meet criteria for anxiety and about 19% for depression. The inability to eat, work, or care for yourself for weeks or months takes a real toll on mental health, relationships, and finances. Some women with HG terminate otherwise wanted pregnancies because the suffering is unbearable, and others decide against future pregnancies entirely despite wanting more children.
The good news is that for most women, the psychological burden lifts as the physical symptoms resolve. But the experience can leave lasting emotional effects, and many women describe feeling dismissed or minimized by people who equate HG with “a little morning sickness.” The identification of GDF15 as a biological driver has been an important validation for the HG community, reinforcing that this condition has a clear physiological basis and is not something women can simply will away.