Hyperemesis gravidarum (HG) is a pregnancy complication that is characterized by severe nausea, vomiting, weight loss, and possibly dehydration. Feeling faint may also occur. It is considered more severe than morning sickness. Symptoms often get better after the 20th week of pregnancy but may last the entire pregnancy duration.

The exact causes of hyperemesis gravidarum are unknown. Risk factors include the first pregnancy, multiple pregnancy, obesity, prior or family history of HG, and trophoblastic disorder.

Diagnosis is usually made based on the observed signs and symptoms. HG has been technically defined as more than three episodes of vomiting per day such that weight loss of 5% or three kilograms has occurred and ketones are present in the urine. Other potential causes of the symptoms should be excluded, including urinary tract infection and an overactive thyroid.

Treatment includes drinking fluids and a bland diet. Recommendations may include electrolyte-replacement drinks, thiamine, and a higher protein diet. Some people require intravenous fluids. With respect to medications, pyridoxine or metoclopramide are preferred. Prochlorperazine, dimenhydrinate, ondansetron (sold under the brand-name Zofran) or corticosteroids may be used if these are not effective. Hospitalization may be required due to the severe symptoms associated. Psychotherapy may improve outcomes. Evidence for acupressure is poor.

While vomiting in pregnancy has been described as early as 2,000 BC, the first clear medical description of HG was in 1852 by Paul Antoine Dubois. HG is estimated to affect 0.3–2.0% of pregnant women, although some sources say the figure can be as high as 3%. While previously known as a common cause of death in pregnancy, with proper treatment this is now very rare. Those affected have a lower risk of miscarriage but a higher risk of premature birth. Some pregnant women choose to have an abortion due to HG symptoms.