HG during pregnancy stands for hyperemesis gravidarum, a severe form of nausea and vomiting that goes far beyond typical morning sickness. It’s characterized by persistent vomiting, loss of more than 5% of your pre-pregnancy body weight, dehydration, and an inability to keep food or fluids down. HG is one of the leading causes of hospitalization in early pregnancy.
How HG Differs From Morning Sickness
Up to 80% of pregnant people experience some nausea during the first trimester. That’s normal. It tends to start around four weeks after the last menstrual period, peak around nine weeks, and fade as the second trimester begins. HG follows a similar timeline but is dramatically more intense. Instead of occasional queasiness or vomiting that you can manage with crackers and rest, HG makes it nearly impossible to eat or drink at all.
The key differences are severity and consequences. With ordinary morning sickness, you can still get through your day and maintain your weight. With HG, the vomiting is relentless enough to cause significant weight loss, dry mouth, constipation, extreme fatigue, and a complete inability to perform daily activities. About 60% of all pregnancy nausea cases resolve by the end of the first trimester, and 87% resolve by 20 weeks. HG can persist longer and often requires medical treatment before it improves.
What Causes It
For decades, the exact cause of HG was unclear. A major breakthrough came from research identifying a protein called GDF15, which is produced by the fetus and released into the mother’s bloodstream starting in early pregnancy. Higher circulating levels of GDF15 are directly associated with more severe nausea and vomiting.
What makes some people develop HG while others barely feel nauseated comes down to sensitivity. If your body is accustomed to low levels of GDF15 before pregnancy (partly determined by your genetics), you’re more vulnerable to the sudden surge that happens once the fetus starts producing it. Think of it like a sudden blast of bright light after sitting in a dark room: the contrast makes the reaction more extreme. People who carry genetic variants associated with naturally low GDF15 levels before pregnancy face a higher risk of developing HG.
How HG Is Diagnosed
There’s no single test for HG. Doctors diagnose it clinically by looking at the full picture: early-onset severe vomiting, substantial weight loss (typically 5% or more of your pre-pregnancy weight), visible signs of dehydration, and lab work that backs it up. Other possible causes of vomiting, like thyroid problems or gastrointestinal conditions, need to be ruled out first.
Lab results in HG typically show signs of dehydration and electrolyte imbalances, including low sodium, low potassium, and elevated kidney markers. Ketones in the urine are a common finding, signaling that your body has shifted to burning fat for energy because you can’t keep food down. While ketones alone don’t confirm HG, both the American College of Obstetricians and Gynecologists (ACOG) and the Society of Obstetricians and Gynaecologists of Canada use them as a supporting indicator of severity.
What Treatment Looks Like
Mild cases may be managed at home with anti-nausea medications, but many people with HG end up needing IV fluids in a clinic or hospital to correct dehydration and restore electrolyte balance. The goal is to stop the vomiting cycle, rehydrate you, and get you back to tolerating food.
Several anti-nausea medications are used, and doctors often try more than one to find what works. Some target the brain’s nausea center directly, while others work on the gut. Research comparing common options found that they tend to have similar effectiveness at controlling vomiting, but differ in side effects. Some cause significant drowsiness and dizziness, while newer options are better tolerated. If standard anti-nausea drugs aren’t enough, corticosteroids (which act on the vomiting center in the brain) are sometimes used for severe, treatment-resistant cases. In one study, vomiting stopped within three hours of the first IV steroid dose. However, steroids are generally reserved as a last resort, used only after vomiting has continued for more than four weeks with ongoing dehydration and other treatments have failed.
Risks if HG Goes Untreated
When HG is properly managed, most pregnancies have good outcomes. But prolonged, untreated vomiting carries real risks for both the mother and baby.
For the baby, a meta-analysis of over 172,000 pregnancies found that people with severe vomiting had a higher risk of delivering babies with low birth weight and growth restriction. The risk of preterm birth, however, was not significantly increased.
For the mother, the most serious complication is a neurological condition caused by severe thiamine (vitamin B1) deficiency. When weeks of vomiting deplete the body’s thiamine stores, the brain can’t function properly. Symptoms include confusion, lethargy, difficulty walking, and abnormal eye movements. This condition is rare but serious, and it’s often misdiagnosed because doctors may not expect it in a young, otherwise healthy pregnant person. More than half of HG patients who develop this complication also show liver function abnormalities from prolonged nutritional deprivation. Severe dehydration can also lead to kidney injury when the kidneys don’t receive enough fluid to filter properly.
The Emotional Toll
HG is not just physically debilitating. Many people describe feeling isolated, dismissed, or told that their symptoms are normal or psychological. Being unable to eat, work, or care for yourself or other children for weeks or months takes a significant mental health toll. The condition can strain relationships and sometimes influences decisions about future pregnancies.
One of the most frustrating aspects of HG is that it’s invisible to others. You may look fine between vomiting episodes, which can make it harder for family, employers, and even some healthcare providers to grasp how disabling it is. If your symptoms are severe enough to prevent you from keeping fluids down, losing weight rapidly, or functioning day to day, that warrants aggressive treatment, not reassurance that it will pass on its own.
What Recovery Looks Like
For most people, HG symptoms gradually ease as pregnancy progresses. The majority see significant improvement by 20 weeks, though a smaller percentage deal with symptoms into the third trimester or even up to delivery. Recovery isn’t always linear. You might have a good stretch followed by a flare-up, especially if you try to reduce medications too quickly.
After delivery, symptoms typically resolve rapidly. However, some people experience lingering food aversions, anxiety around eating, or symptoms resembling post-traumatic stress, particularly after severe or prolonged cases. If you’ve had HG in one pregnancy, the risk of recurrence in future pregnancies is elevated, which is an important factor in family planning.