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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Severe NVP with >5% weight loss, dehydration, ketonuria, and electrolyte disturbance
- Peaks at 8–12 weeks, usually resolves by 16–20 weeks
- Exclude other causes: UTI, molar pregnancy, thyrotoxicosis, raised intracranial pressure
- First-line antiemetic: cyclizine 50 mg TDS or prochlorperazine 5–10 mg TDS. Ondansetron second-line
- IV fluid rehydration with normal saline + KCl. AVOID dextrose until thiamine given (Wernicke risk)
- Give IV thiamine 100 mg before any dextrose-containing fluids
Overview
Hyperemesis gravidarum (HG) is a severe form of nausea and vomiting in pregnancy characterised by persistent vomiting leading to weight loss (>5% of pre-pregnancy weight), dehydration, and electrolyte imbalance. It is distinct from the common nausea and vomiting of pregnancy (NVP), which affects 70–80% of pregnancies but is typically self-limiting. HG is thought to be related to rapidly rising hCG and oestrogen levels, with genetic susceptibility playing a role. It is more common with molar pregnancy (markedly elevated hCG) and multiple pregnancy.
Epidemiology
HG affects approximately 0.3–3.6% of pregnancies, depending on definition. It is a leading cause of hospital admission in early pregnancy. Risk factors include previous HG, multiple pregnancy, molar pregnancy, family history, and history of motion sickness or migraine. It typically begins at 6–8 weeks, peaks at 8–12 weeks, and resolves by 16–20 weeks in most cases, although some women are affected throughout pregnancy.
Clinical Features
Symptoms
Persistent, severe nausea and vomiting — unable to tolerate oral intake
Weight loss >5% of pre-pregnancy weight
Inability to keep down fluids or food
Excessive salivation (ptyalism)
Fatigue, weakness, dizziness
Symptoms significantly worse than typical NVP and impacting daily life
Signs
Dehydration: dry mucous membranes, reduced skin turgor, tachycardia, postural hypotension
Ketonuria on urine dipstick
Weight loss documented at clinic visits
Signs of Wernicke encephalopathy (if prolonged and thiamine-deficient): confusion, ataxia, ophthalmoplegia
Investigations
First-line
Urine dipstickKetonuria confirms significant starvation and dehydration. Also check for UTI
U&EsHypokalaemia, hyponatraemia, hypochloraemic metabolic alkalosis from vomiting
FBCHaemoconcentration (raised haematocrit) from dehydration
WeightCompare to pre-pregnancy weight — >5% loss supports HG diagnosis
Second-line
TFTsTransient thyrotoxicosis (hCG has structural similarity to TSH) — suppressed TSH, mildly raised fT4. Usually resolves spontaneously
LFTsMildly deranged in up to 50% of HG admissions
Pelvic USSIf not already had dating scan — exclude molar pregnancy and multiple pregnancy
Specialist
PUQE scorePregnancy-Unique Quantification of Emesis — validated tool to assess severity (mild ≤6, moderate 7–12, severe ≥13)
1
Mild (outpatient)
- Reassurance and dietary advice: small frequent meals, avoid triggers, dry bland foods
- Ginger supplements or P6 acupressure wristbands (limited evidence but safe)
- First-line antiemetics: cyclizine 50 mg PO/IM/IV TDS or prochlorperazine 5–10 mg PO TDS (or 12.5 mg IM)
- If first-line inadequate: ondansetron 4–8 mg PO/IV BD (note: small risk of cleft palate in first trimester)
2
Moderate-severe (inpatient)
- IV fluid rehydration: normal saline with potassium chloride (20–40 mmol/L). Avoid dextrose initially
- IV thiamine 100 mg BEFORE any dextrose-containing fluids (prevents Wernicke encephalopathy)
- Parenteral antiemetics: cyclizine 50 mg IV TDS, or ondansetron 4 mg IV BD
- Correct electrolyte abnormalities (especially potassium)
- Thromboprophylaxis: LMWH if immobilised and dehydrated — high VTE risk
3
Refractory cases
- Consider corticosteroids: hydrocortisone 100 mg IV BD, converting to prednisolone 40 mg PO tapering. Use only after specialist review and after 12 weeks
- Total parenteral nutrition (TPN) in extreme cases
- Psychological support — HG causes significant distress, anxiety, and depression
Complications
- Wernicke encephalopathy: From thiamine (B1) deficiency — confusion, ataxia, ophthalmoplegia. Give thiamine BEFORE dextrose
- Mallory-Weiss tear: From forceful vomiting — presents with haematemesis
- Electrolyte disturbance: Hypokalaemia, hyponatraemia — may cause cardiac arrhythmia
- Psychological: Depression, anxiety, social isolation, consideration of pregnancy termination
- IUGR: If severe and prolonged — though most women have normal fetal outcomes
UKMLA Exam Tips
- 1HG = NVP + >5% weight loss + dehydration + ketonuria. NVP alone is NOT HG
- 2Give IV thiamine BEFORE dextrose — Wernicke encephalopathy is a preventable complication
- 3First-line antiemetics: cyclizine or prochlorperazine. Ondansetron is second-line
- 4Rehydrate with normal saline + KCl initially, NOT dextrose-saline
- 5hCG cross-reacts with TSH receptor → transient gestational thyrotoxicosis. Do NOT treat with antithyroid drugs
- 6Molar pregnancy causes very high hCG and is associated with severe HG — always USS
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