Nausea/vomiting in pregnancy
Exam Tips
- Timing is high yield: classic NVP starts early first trimester; new onset after 11 weeks should trigger search for another cause.
- Use PUQE score in OSCEs to structure severity assessment and escalation decisions.
- Always ask about urine output, weight change, oral intake, mental health impact, and function at home/work.
- In severe vomiting, remember thiamine before dextrose to prevent Wernicke encephalopathy.
- If dehydrated or admitted, include VTE risk assessment and prophylaxis planning in your management answer.
Definition
Nausea and vomiting in pregnancy (NVP) is a clinical diagnosis when symptoms begin early in gestation (typically 4-7 weeks), other causes are excluded, and severity ranges from mild nausea to frequent vomiting that impairs intake. Symptoms usually peak around 9-16 weeks and settle by 16-20 weeks; onset after about 11 weeks should prompt active consideration of alternative pathology. Hyperemesis gravidarum is the severe end of the spectrum, with inability to maintain oral hydration/nutrition, dehydration, and major functional limitation.
Pathophysiology
NVP is multifactorial. Current evidence supports a placental-biological mechanism, with growth differentiation factor 15 (GDF15) strongly associated with hyperemesis risk and recurrence, while human chorionic gonadotrophin (hCG) appears temporally related but less likely to be the primary driver. Hormonal and gastrointestinal contributors include high oestrogen states and progesterone-mediated smooth-muscle relaxation causing delayed gastric emptying and dysmotility. Genetic susceptibility (including family clustering), central emetic pathway sensitivity, and possibly Helicobacter pylori-associated inflammation may further amplify symptoms in severe disease.
Risk Factors
- Previous hyperemesis gravidarum (strong recurrence risk)
- First pregnancy
- Multiple pregnancy or molar pregnancy (greater placental mass)
- Family history in a first-degree relative
- History of motion sickness or migraine
- Nausea with oestrogen-containing contraception
- Obesity
- Possible chronic Helicobacter pylori infection
Clinical Features
Symptoms
- Persistent nausea (not limited to mornings)
- Vomiting and/or retching with reduced oral intake
- Reduced urine output or dark urine suggesting dehydration
- Weight loss, fatigue, poor sleep
- Functional impairment (work/home/social/caring roles)
- Psychological distress, anxiety, low mood
- Red-flag associated symptoms suggesting alternative diagnosis: abdominal pain, fever, urinary symptoms, headache, focal neurological symptoms
Signs
- Dry mucous membranes
- Tachycardia
- Postural hypotension
- Weight loss or muscle wasting
- Abdominal tenderness (suggests alternative cause)
- Neurological signs of thiamine deficiency/Wernicke encephalopathy (confusion, ataxia, nystagmus)
- Fever (suggests infection/other pathology)
Investigations
Management
Lifestyle Modifications
- Explain natural history and safety-net red flags; review within 24-72 hours if intake is poor
- Small frequent meals, avoid triggers (odours/fatty/spicy foods), maintain oral fluids with frequent sips
- Psychosocial support and assessment of mood, coping, and safeguarding needs
- Stop or reduce aggravating medicines where possible (for example oral iron, opioids)
- Escalate to ambulatory/day-unit or inpatient care if dehydration, weight loss, or inability to tolerate oral therapy
Pharmacological Treatment
First-line antihistamine/phenothiazine options
- Cyclizine 50 mg PO/IM/IV up to three times daily
- Prochlorperazine 5-10 mg PO two to three times daily (or buccal 3 mg twice daily)
- Promethazine 10-25 mg PO at night or 10 mg twice daily
- Chlorpromazine 10-25 mg PO every 4-6 hours (or IM/IV in specialist care)
Use regular dosing, then step-up/combination if needed. Warn about sedation and anticholinergic effects; avoid driving if drowsy. Phenothiazines/metoclopramide can cause extrapyramidal reactions.
Second-line/prokinetic or 5-HT3 antagonist
- Metoclopramide 5-10 mg PO/IV three times daily (maximum 5 days)
- Ondansetron 4-8 mg PO/IV twice daily (sometimes three times daily in specialist care)
Metoclopramide duration is restricted due to neurological adverse effects (including dystonia). Ondansetron is widely used when first-line fails; discuss limited but evolving first-trimester safety data and monitor QT-risk factors.
Combination delayed-release doxylamine/pyridoxine
- Doxylamine 10 mg/pyridoxine 10 mg gastro-resistant tablets: start 2 tablets at night; increase stepwise to max 4 tablets/day (1 morning, 1 mid-afternoon, 2 at night)
Useful for persistent symptoms despite simple measures. Counsel regarding somnolence; avoid alcohol and other CNS depressants.
Supportive therapy in severe hyperemesis
- IV 0.9% sodium chloride with potassium chloride (guided by U&Es)
- Thiamine 100 mg orally two to three times daily, or IV thiamine/Pabrinex before carbohydrate/dextrose administration
- Low-molecular-weight heparin prophylaxis (for admitted women unless contraindicated)
Do not give dextrose-containing fluids before thiamine because of risk of precipitating Wernicke encephalopathy. Monitor fluid balance, renal function, and electrolytes closely. Check LMWH contraindications (active bleeding, severe thrombocytopenia, high bleeding risk).
Complications
- Dehydration and electrolyte disturbance (hyponatraemia, hypokalaemia, hypochloraemic alkalosis; severe cases may develop acidaemia)
- Acute kidney injury
- Malnutrition and vitamin deficiency (notably thiamine deficiency causing Wernicke encephalopathy; B6/B12-related neuropathy)
- Abnormal liver enzymes
- Gastro-oesophageal injury (reflux, oesophagitis, gastritis, Mallory-Weiss tear; very rarely oesophageal rupture)
- Rare pressure-related complications (pneumomediastinum/pneumothorax, retinal haemorrhage)
- Venous thromboembolism risk increased by dehydration and immobility
- Major psychosocial morbidity (depression, anxiety, PTSD, suicidal ideation) and reduced quality of life
- Fetal risk rises mainly when severe hyperemesis is associated with poor maternal weight gain (preterm birth, low birthweight, small for gestational age)
Prognosis
Most mild-moderate NVP improves by 16-20 weeks, though a minority continue into late pregnancy. Hyperemesis can be prolonged and debilitating but congenital anomaly risk is not clearly increased; adverse fetal outcomes are mainly linked to severe maternal disease with inadequate weight gain. Recurrence in future pregnancies is common, with studies reporting a wide range (approximately 15-81%) because of differing definitions and populations.
Sources & References
🏥BMJ Best Practice(2)
💊BNF Drug References(7)
- Chlorpromazine hydrochloride[management.pharmacological]
- Cinnarizine[management.pharmacological]
- Cyclizine[management.pharmacological]
- Doxylamine with pyridoxine[management.pharmacological]
- Levomepromazine[management.pharmacological]
- Metoclopramide hydrochloride[management.pharmacological]
- Prochlorperazine[management.pharmacological]
✅NICE Guidelines(1)
- Nausea/vomiting in pregnancy[overview]