Hyperemesis gravidarum (HG) is a severe pregnancy condition causing persistent vomiting, dehydration, and weight loss. It affects 1 to 3% of pregnancies and goes far beyond normal morning sickness. Treatment includes antiemetic medication, IV fluids, and in severe cases hospitalisation. HG can have a significant impact on mental health. If you cannot keep any food or fluids down for 24 hours, contact your GP or maternity unit urgently.
Hyperemesis gravidarum (HG) is a severe pregnancy condition characterised by persistent, excessive nausea and vomiting that leads to dehydration and weight loss. It is far more severe than typical morning sickness and can be debilitating, sometimes requiring hospital admission for intravenous fluids and medication.
According to the RCOG, HG affects 1 to 3 in every 100 pregnancies. It typically begins between weeks 4 and 7 of pregnancy and can persist well into the second trimester or, in some cases, throughout the entire pregnancy. It was brought to wider public attention when Catherine, Princess of Wales, experienced it during her pregnancies.
While morning sickness causes intermittent nausea that is manageable with dietary changes, HG is on a different scale entirely:
Persistent vomiting. Vomiting multiple times a day, often unable to keep any food or fluids down. This is not occasional retching — it is relentless.
Severe dehydration. Dark urine, dry mouth, dizziness on standing, rapid heartbeat, and reduced urination are all signs that vomiting is causing significant fluid loss.
Weight loss. Losing more than 5% of pre-pregnancy body weight is a common diagnostic marker. Some people lose significantly more.
Ketosis. When your body breaks down fat for energy because it cannot get enough from food. Ketones in the urine are tested during assessment.
Inability to function normally. HG can make it impossible to work, care for other children, or carry out daily activities. Many people with HG are effectively bedbound during the worst periods.
Research published in Nature in 2024 identified a hormone called GDF15 as a key driver of HG. GDF15 levels rise in pregnancy, and people with lower pre-pregnancy exposure to this hormone (meaning they are less desensitised to it) appear more susceptible to severe nausea. This discovery was a breakthrough in understanding why some people experience debilitating sickness while others do not.
Other contributing factors include very high levels of hCG (which peak around weeks 8 to 10), multiple pregnancy (twins or more increase hCG levels), a family history of HG (there is a strong genetic component), and a personal history of HG in a previous pregnancy (recurrence rates are high).
First-line: antiemetic medication. The RCOG recommends early treatment with antiemetic medication. Commonly prescribed options in the UK include cyclizine, prochlorperazine, metoclopramide, and ondansetron. These are prescribed in a stepwise approach — if one does not work, another is tried. All have been assessed for safety in pregnancy.
IV fluids. If you are severely dehydrated or have not been able to keep fluids down, you may need intravenous fluid replacement in hospital or via ambulatory care (day assessment units). IV fluids restore hydration and correct electrolyte imbalances.
Thiamine (vitamin B1). Prolonged vomiting can deplete thiamine levels, increasing the risk of Wernicke''s encephalopathy, a serious neurological condition. The RCOG recommends thiamine supplementation for anyone with prolonged vomiting.
Steroid therapy. In severe cases that do not respond to standard antiemetics, corticosteroids (such as hydrocortisone or prednisolone) may be considered. This is a specialist treatment used in refractory HG.
Hospitalisation. If outpatient treatment is insufficient, hospital admission allows for continuous IV fluids, regular antiemetic medication, monitoring of ketones and electrolytes, and nutritional support.
HG can have a devastating effect on mental health. Research by the Pregnancy Sickness Support charity found that 49% of people with HG considered terminating an otherwise wanted pregnancy due to the severity of their symptoms. Depression, anxiety, isolation, and feelings of guilt are all common.
If you are struggling emotionally, speak to your midwife or GP about perinatal mental health support. You are not weak for finding HG unbearable — it is a severe medical condition, not a failure of willpower.
Pregnancy Sickness Support (pregnancysicknesssupport.org.uk) is a UK charity that provides a helpline, support forum, and resources specifically for people with HG. The HER Foundation (hyperemesis.org) offers international resources and advocacy. Your midwife or GP can also refer you to perinatal mental health services if needed.
If you have had HG in one pregnancy, the recurrence rate in subsequent pregnancies is high (estimated at 50 to 80%). However, knowing what to expect and starting treatment early can make a significant difference. Speak to your GP before conceiving again so that a management plan can be put in place from the start.
Diagnosis is based on persistent vomiting with dehydration and weight loss (typically more than 5% of pre-pregnancy weight). Your doctor will test urine for ketones and may run blood tests to check electrolytes.
If untreated, severe dehydration and nutritional deficiency can be harmful. With proper treatment including medication, IV fluids, and monitoring, most people with HG have healthy pregnancies. Early treatment is key.
For most people, symptoms improve by 16 to 20 weeks. However, some experience HG throughout the entire pregnancy. Even if it improves, mild nausea may persist longer than with typical morning sickness.
Yes. The RCOG recommends early treatment with antiemetic medication for HG. Cyclizine, prochlorperazine, and ondansetron are commonly prescribed and have been assessed for safety in pregnancy.
The recurrence rate is estimated at 50 to 80%. However, starting treatment early in a subsequent pregnancy can significantly reduce severity. Speak to your GP before conceiving to have a plan in place.
Milestones, partner sharing, notes, photos, and a curated essentials guide. Free, no app to install.
Get Started Free© 2026 Nuhah. All rights reserved.