What is hyperemesis gravidarum (severe morning sickness)?

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Hyperemesis gravidarum is a severe form of nausea and vomiting in pregnancy. (1) In fact, the words ‘hyperemesis’ (pronounced ‘hye-pur-em-ee-sis’) and ‘gravidarum’ (pronounced ‘gra-vid-ah-room’) literally translate to ‘excessive vomiting’ ‘during pregnancy’. (10)

What are the symptoms of hyperemesis gravidarum (HEG)?

The main symptoms of hyperemesis gravidarum are:

  • continued and severe nausea and vomiting – particularly if vomiting occurs more than 3-4 times a day and prevents one from keeping down food or fluids
  • weight loss – which may be over 10% of body weight
  • nutritional deficiencies
  • infrequent urination
  • dehydration – which in turn may cause headaches, palpitations, confusion and hypotension (low blood pressure) when standing
  • fainting
  • feeling tired and dizzy
  • ketosis caused by a raised number of poisonous acidic chemicals in the blood
  • pale skin
  • jaundice
  • muscle wasting
  • Ptyalism – excessive secretion of saliva (1-4, 13)

How long does hyperemesis gravidarum last?

Hyperemesis gravidarum can last much longer than normal morning sickness – which tends to settle down around 12-14 weeks of pregnancy. Hyperemesis gravidarum generally diminishes around 21 weeks into the pregnancy, but it may continue much longer. (1, 2)

What causes hyperemesis gravidarum?

There are several theories regarding what causes hyperemesis gravidarum. Some theories concern the hormonal changes that occur in pregnancy. In particular, theories focus on the increase in human chorionic gonadotropin (hCG). This hormone is said to be associated with the peak in symptoms of morning sickness. There have been difficulties with directly demonstrating a link between hCG concentrations and severity of morning sickness however due to the variation in hCG concentrations in the population. (2, 3, 5)

Other potential causes of hyperemesis gravidarum include:

  • emotional changes
  • nutritional deficiencies – in particular a deficiency in vitamin B6
  • gastric problems
  • increased estrogen levels (1, 2)

How common is hyperemesis gravidarum?

According to the NHS, hyperemesis gravidarum is thought to affect around 1 in 200 women. (1) Estimates do, however, vary depending on how hyperemesis gravidarum is defined. The estimated incidence rates of severe morning sickness tend to be between 0.5% and 2% of pregnancies. (1, 3, 4)

Who is most likely to develop hyperemesis gravidarum?

Certain women are more likely to develop hyperemesis gravidarum than others. These include:

  • women who suffer from migraines
  • women who have previously suffered from motion sickness
  • those with a family history of hyperemesis gravidarum
  • women with a multiple pregnancy – such as twins or triplets
  • increased bodyweight
  • a female fetus
  • women who have had hyperemesis gravidarum in a previous pregnancy
  • molar pregnancies – where a mass of abnormal cells (referred to as a “mole”) grow instead of the normally developing baby
  • fetal anomalies e.g. trisomy 21 and hydrops fetalis (6-9)

How is hyperemesis gravidarum diagnosed?

Diagnosis of hyperemesis gravidarum involves:

  • determining weight loss - via weight measurement
  • determining electrolyte imbalance - via blood tests

A doctor may also assess overall condition, such as ability to perform daily activities and psychological state of mind. Many women with hyperemesis gravidarum feel ambivalent towards their pregnancy due to their symptoms. (4, 6, 7)

It is also important for other causes of the symptoms of hyperemesis gravidarum to be ruled out. In particular, the following causes should be dismissed:

  • gastrointestinal problems – such as gastric outlet obstruction from peptic ulcer disease
  • metabolic disorders such as thyroid problems
  • diabetic ketoacidosis
  • Addison’s disease
  • hypercalcemia
  • liver problems – such as viral hepatitis
  • kidney stones
  • urinary tract infection
  • neurological disorders
  • migraines
  • molar pregnancy
  • HELLP syndrome
  • pancreatitis
  • appendicitis
  • gallbladder disease (3, 11, 12, 13)

How is hyperemesis gravidarum treated?

In the early stages of hyperemesis gravidarum, the following is advised:

  • rest
  • eating small pieces of dry toast, crackers, or bananas before getting out of bed
  • consuming ginger-containing foods or drinks
  • eating small meals several times a day and not allowing yourself to get too hungry or too full
  • eating a diet high in protein and complex carbohydrates and low in fatty foods
  • eating bland or dry foods
  • drinking plenty of water
  • acupressure on the inside of the wrist – this may be done by pressing a finger against the wrist or wearing a special wristband
  • anti-nausea medications may be prescribed by a doctor, however, it is important that the potential benefits and risks have first been considered (2, 3, 4, 10)

For more severe cases of hyperemesis gravidarum, hospitalization for a few days may be necessary. Whilst in hospital the following treatments may be given:

  • intravenous (IV) fluids to treat dehydration
  • parental nutrition (nutrition by vein)
  • treatment for ketosis (1, 2, 3, 4)

Is hyperemesis gravidarum harmful to your baby?

In most mild cases of hyperemesis gravidarum no harm is caused to the baby. However, severe hyperemesis gravidarum, in particular the weight loss and nutritional deficiencies, may cause problems for fetal growth. This may lead to the baby being born with a low birth weight.

Other problems that may occur as a result of severe hyperemesis gravidarum include:

  • premature labor
  • pre-eclampsia
  • Mallory-Weiss tears – tears to the stomach due to excessive vomiting
  • Wernicke’s encephalopathy – which causes disorientation, confusion and potentially coma due to a lack of thiamin (1, 2, 3, 6)

If you experience hyperemesis gravidarum in your first pregnancy, will you necessarily experience it in a future pregnancy?

It is thought that around two-thirds of women who experience hyperemesis gravidarum in their first pregnancy will also experience it in a future pregnancy. (14)

Further Reading

Last Updated: May 19, 2023

April Cashin-Garbutt

Written by

April Cashin-Garbutt

April graduated with a first-class honours degree in Natural Sciences from Pembroke College, University of Cambridge. During her time as Editor-in-Chief, News-Medical (2012-2017), she kickstarted the content production process and helped to grow the website readership to over 60 million visitors per year. Through interviewing global thought leaders in medicine and life sciences, including Nobel laureates, April developed a passion for neuroscience and now works at the Sainsbury Wellcome Centre for Neural Circuits and Behaviour, located within UCL.


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