Hyperemesis Gravidarum: When Pregnancy Sickness Becomes Severe
Feeling sick or vomiting during pregnancy is extremely common. It is often called “morning sickness”, although this name can be misleading because nausea and vomiting can happen at any time of the day or night.
For most women, pregnancy sickness is uncomfortable but manageable. However, for some, the symptoms become much more severe and can interfere with eating, drinking and everyday life. This severe form of pregnancy sickness is called hyperemesis gravidarum, often shortened to HG.
According to the Royal College of Obstetricians and Gynaecologists (RCOG), nausea and vomiting in pregnancy affects up to 90% of pregnant women, while hyperemesis gravidarum affects approximately 0.3% to 3.6% of pregnancies.
What is hyperemesis gravidarum?
Hyperemesis gravidarum is much more than simply feeling sick during pregnancy.
It is a severe form of pregnancy-related nausea and vomiting that can make it difficult to eat and drink normally and can significantly affect a woman’s ability to carry out normal daily activities.
Pregnancy sickness usually begins early in pregnancy, often between around 4 and 7 weeks. For about 90% of women, symptoms have settled by 20 weeks, although some women may continue to experience symptoms for longer.
RCOG defines nausea and vomiting of pregnancy as symptoms beginning before 16 weeks of pregnancy, once other possible causes of nausea and vomiting have been considered.
How common is it?
| Condition | How common is it? |
|---|---|
| Nausea and vomiting during pregnancy | Up to 90% of pregnancies |
| Hyperemesis gravidarum | Around 0.3–3.6% of pregnancies |
Although HG affects a relatively small proportion of pregnancies, it can have a major effect on physical health, emotional wellbeing, work, family life and quality of life.
How severe is pregnancy sickness?
Doctors may use questionnaires to help measure how severe symptoms are.
One commonly used system is the Pregnancy-Unique Quantification of Emesis score, usually called the PUQE score.
It looks at three things over the previous 24 hours:
- how long you have felt nauseated
- how many times you have vomited
- how often you have experienced retching or dry heaving.
The total score ranges from 3 to 15.
| PUQE score | Severity |
|---|---|
| 3–6 | Mild |
| 7–12 | Moderate |
| 13–15 | Severe |
Another assessment tool called the HELP score may also be used, particularly in women with more severe symptoms or hyperemesis gravidarum.
These scores help healthcare professionals understand how badly someone is affected and whether treatment is working.
An important change in how HG is diagnosed
In the past, hyperemesis gravidarum was often diagnosed only when a woman had lost more than 5% of her pre-pregnancy weight, was dehydrated and had abnormal blood salt levels.
The current RCOG guideline no longer requires all of these features to be present before HG can be diagnosed.
This means women should not have to become severely dehydrated or lose large amounts of weight before their symptoms are taken seriously.
What about ketones in the urine?
Women with severe pregnancy sickness have traditionally had their urine tested for ketones.
However, the latest RCOG guideline says that ketones in the urine should not be used to judge how dehydrated someone is or how severe their hyperemesis is.
A woman can therefore be very unwell even if her urine ketone result does not appear particularly abnormal.
How is hyperemesis gravidarum treated?
Treatment depends on how severe the symptoms are, whether the woman can drink and eat, whether she is dehydrated and whether treatment at home is working.
The aim is to:
- control nausea and vomiting
- prevent dehydration
- correct salt and electrolyte problems
- prevent vitamin deficiencies
- maintain nutrition
- reduce complications
- allow the woman to eat, drink and function as normally as possible.
Mild pregnancy sickness
Many women with mild symptoms can be treated at home.
Simple measures may include:
- eating small amounts regularly
- avoiding long periods with an empty stomach
- drinking small amounts frequently
- avoiding foods or smells that trigger nausea
- taking anti-sickness medication if needed.
Importantly, women do not need to wait until pregnancy sickness becomes severe before asking for treatment.
Anti-sickness medicines
Several anti-sickness medicines can be used during pregnancy.
RCOG recommends a number of medicines as first-line treatments, including:
- doxylamine with pyridoxine
- cyclizine
- promethazine
- prochlorperazine
- chlorpromazine.
If these do not control symptoms adequately, other medicines may be considered, including:
- metoclopramide
- ondansetron
- domperidone.
Sometimes a combination of medicines works better than using just one medicine.
A doctor, midwife or other appropriate healthcare professional should advise which medicine is most suitable.
What about ondansetron?
Ondansetron is an effective anti-sickness medicine and is commonly used when first-line treatments have not worked.
RCOG advises that women should not be discouraged from using ondansetron when other treatments have been ineffective.
Some studies suggest a very small increase in the risk of cleft lip or palate when ondansetron is taken during the first trimester.
RCOG describes the estimated risk as approximately:
| Orofacial cleft | Incidence |
|---|---|
| Without ondansetron | Around 11 in 10,000 births |
| After first-trimester ondansetron exposure | Around 14 in 10,000 births |
This represents around 3 additional cases for every 10,000 births.
For women with severe vomiting, this very small possible risk needs to be weighed against the risks of leaving severe hyperemesis inadequately treated.
When might hospital treatment be needed?
Hospital admission is not necessary for everyone with HG.
However, hospital assessment or admission may be recommended if you:
- cannot keep fluids down
- cannot keep anti-sickness tablets down
- are becoming dehydrated
- are losing significant weight despite treatment
- have abnormal blood tests or electrolyte levels
- have another medical condition that is being affected because you cannot take your usual medication
- have an infection that requires treatment you cannot tolerate by mouth
- continue to be unwell despite treatment through an ambulatory or day-care service.
Some hospitals offer ambulatory day-care treatment, allowing women to receive intravenous fluids and medication without needing to stay in hospital overnight.
Intravenous fluids
If dehydration develops, fluids may need to be given directly into a vein through a drip.
RCOG recommends 0.9% sodium chloride, usually with potassium added when appropriate, depending on blood test results.
Women receiving intravenous fluids should have their electrolytes monitored.
Glucose-containing fluids are not routinely used for rehydration in HG because giving glucose to someone who is severely deficient in vitamin B1 can contribute to a serious neurological condition called Wernicke encephalopathy.
Why is thiamine important?
Women who have been vomiting for a prolonged period or eating very little can become deficient in thiamine, or vitamin B1.
Severe thiamine deficiency can lead to Wernicke encephalopathy, which affects the brain and nervous system.
For this reason, RCOG recommends thiamine supplementation for women admitted to hospital with prolonged vomiting or severely reduced food intake.
Thiamine is particularly important before giving glucose-containing intravenous fluids or artificial nutrition.
What if anti-sickness medicines do not work?
A small number of women continue to experience severe symptoms despite several anti-sickness medicines and intravenous fluids.
In these situations, corticosteroids may sometimes be considered.
Steroids are generally reserved for severe, persistent hyperemesis that has not responded to standard treatments.
They are usually started under specialist supervision and the dose is gradually reduced once symptoms improve.
Preventing blood clots
Pregnancy itself slightly increases the risk of developing a blood clot.
Being dehydrated, unwell and less mobile because of hyperemesis can increase this risk further.
Women admitted to hospital because of HG are therefore usually offered injections of a blood-thinning medicine called low-molecular-weight heparin (LMWH) unless there is a medical reason why it cannot be given.
What if eating remains impossible?
Most women improve with fluids, anti-sickness medication and supportive treatment.
Very occasionally, severe HG continues despite these measures.
If a woman is unable to maintain adequate nutrition, a specialist team may consider additional nutritional support.
This may include:
- nutritional drinks or supplements
- feeding through a tube into the stomach or bowel
- in exceptional circumstances, nutrition given directly into a vein.
These treatments require specialist monitoring because artificial nutrition can itself cause complications.
When should you seek medical help?
Contact your GP, midwife, maternity unit or early pregnancy service if pregnancy sickness is making it difficult for you to eat, drink or carry out normal activities.
More urgent assessment may be needed if you:
- cannot keep fluids down
- are passing very little urine
- feel extremely weak, dizzy or faint
- are losing significant weight
- vomit blood
- develop severe abdominal pain or fever
- cannot keep important regular medication down
- feel that your symptoms are becoming unmanageable.
You do not need to wait until you are severely dehydrated before asking for help.
The key message
Pregnancy sickness is common, but severe pregnancy sickness should not simply be accepted as something you have to endure.
Hyperemesis gravidarum can significantly affect physical and emotional wellbeing, but effective treatments are available.
Early recognition, adequate anti-sickness treatment, hydration and nutritional support can make an enormous difference.
If your symptoms are stopping you from eating, drinking or functioning normally, speak to your healthcare team.
References
1. Royal College of Obstetricians and Gynaecologists (RCOG).
The Management of Nausea and Vomiting in Pregnancy and Hyperemesis Gravidarum. Green-top Guideline No. 69. Second edition. BJOG. First published 4 February 2024.
2. Royal College of Obstetricians and Gynaecologists / BJOG.
Correction to The Management of Nausea and Vomiting in Pregnancy and Hyperemesis Gravidarum (Green-top Guideline No. 69). Published 19 June 2025. This correction clarifies, among other points, that prochlorperazine should not be administered intravenously.
3. Royal College of Obstetricians and Gynaecologists / BJOG.
Correction to The Management of Nausea and Vomiting in Pregnancy and Hyperemesis Gravidarum (Green-top Guideline No. 69). Published 30 June 2026. This corrected the ambulatory treatment algorithm so that 0.9% sodium chloride with 20 mmol potassium chloride is administered over 2 hours, rather than 1–2 hours.
This article is intended for general information and education and does not replace assessment or treatment by your own healthcare professional.