Pregnancy nausea is common and usually manageable. Hyperemesis gravidarum is not manageable – it is incapacitating. Women with HG may be unable to keep any food or fluid down for days or weeks, losing significant weight, becoming dehydrated, and in some cases needing hospital admission with IV fluids and nutritional support. The condition has ended wanted pregnancies and careers, caused relationship breakdown, and led to significant long-term psychological harm including PTSD.
HG has also been historically undertreated and underacknowledged. The message that pregnancy nausea is normal and something to be endured, combined with reluctance to prescribe medication in the first trimester, has left many women without adequate treatment. Greater awareness – including among the women who have it – of what HG actually is, what treatment is available, and what they are entitled to ask for from their healthcare team is long overdue.
Healthbooq (healthbooq.com) covers pregnancy health and complications.
What HG Is and How It Differs From Normal Pregnancy Nausea
Up to 80% of pregnant women experience some nausea in the first trimester, most commonly between weeks 6 and 12. Typical pregnancy nausea often improves with eating small amounts, is worst at certain times of day (despite the "morning sickness" name, it can occur at any time), and does not prevent normal daily function.
Hyperemesis gravidarum is defined by: persistent vomiting that does not resolve with conservative measures; weight loss of 5% or more of pre-pregnancy body weight; dehydration requiring IV fluids; and electrolyte disturbances (hypokalaemia, hyponatraemia, metabolic alkalosis). Women with HG may vomit 20-30 times per day and cannot retain water, let alone food.
The condition most commonly begins around weeks 4-6, peaks at weeks 8-12, and in around 15% of women persists throughout the entire pregnancy.
Causes
The cause of HG is not fully established. Human chorionic gonadotrophin (hCG), which rises rapidly in early pregnancy, is strongly implicated: HG is more common in multiple pregnancies and molar pregnancies where hCG levels are higher. Oestrogen also appears to play a role. Thyroid stimulation (hCG has structural similarity to TSH and can stimulate the thyroid) explains why mild transient hyperthyroidism (gestational thyrotoxicosis) is sometimes found alongside HG.
Helicobacter pylori (H. pylori) infection may be a contributing factor in some cases: studies have found higher H. pylori rates in women with HG, though causation is not established.
Genetic factors appear important: HG recurs in up to 80% of subsequent pregnancies, and having a mother or sister with HG significantly increases risk.
Consequences
Dehydration, electrolyte imbalance, and weight loss in the first trimester affect maternal and, in severe cases, fetal wellbeing. Wernicke's encephalopathy (thiamine deficiency causing neurological damage) is a rare but serious complication of HG that is prevented by thiamine supplementation in women who are unable to eat.
Termination of pregnancy as a consequence of HG has been documented in UK surveys. Pregnancy Sickness Support estimates that HG contributes to a meaningful proportion of terminations in women who would have continued the pregnancy with adequate treatment.
Psychological consequences are significant and often persist beyond the pregnancy: depression, anxiety, PTSD, and tokophobia (fear of pregnancy) are all more common in women who have had HG.
Treatment
Conservative measures (small, frequent meals; avoiding triggers; ginger) are appropriate for typical pregnancy nausea but are insufficient for HG. Women with HG need antiemetic medication.
First-line antiemetics: promethazine, cyclizine, and prochlorperazine are commonly used in the UK. Metoclopramide and domperidone are also used. Ondansetron (a 5-HT3 receptor antagonist) is highly effective for HG and is increasingly prescribed. Earlier concerns about cardiac effects (QT prolongation) and a possible association with cleft palate were raised in some studies; Pregnancy Sickness Support and RCOG guidance note that the available evidence does not establish a significant teratogenic risk from ondansetron, and that for women with severe HG, the risks of untreated dehydration and malnutrition outweigh the risks of treatment.
IV fluids (normal saline or Hartmann's solution with potassium supplementation) for dehydration. Thiamine supplementation to prevent Wernicke's. Nutritional support via nasogastric tube if oral intake cannot be maintained.
NICE guideline NG201 (2021) and RCOG guideline (2016) both address HG management.
Support
Pregnancy Sickness Support (pregnancysicknesssupport.org.uk) provides a peer support helpline, information on treatment options, and guidance on advocating for appropriate care. Women with HG often need to be explicitly supported in asking for adequate treatment.
Key Takeaways
Hyperemesis gravidarum (HG) is severe, intractable nausea and vomiting in pregnancy that causes dehydration, weight loss of more than 5% of pre-pregnancy body weight, and electrolyte disturbances. It is distinct from normal pregnancy nausea (which affects up to 80% of pregnant women) and requires medical treatment. HG affects approximately 1-2% of pregnancies and is a significant cause of hospital admission in the first trimester. The cause is multifactorial and not fully understood; hCG and oestrogen levels are implicated, as is Helicobacter pylori infection in some cases. Treatment involves antiemetic medication (including ondansetron, which is now widely used despite earlier controversy over teratogenicity data), IV fluids, and nutritional support. HG has significant psychological consequences including depression and post-traumatic stress.
