In a 20‑week pregnant woman presenting with dizziness followed by two episodes of vomiting, what are the possible differential diagnoses?

Differential Diagnoses for Dizziness and Vomiting at 20 Weeks Gestation

At 20 weeks gestation with dizziness and vomiting, you must urgently exclude pre-eclampsia and neurological emergencies first, then consider persistent/recurrent nausea and vomiting of pregnancy (NVP), vestibular disorders, and rare complications like thromboembolism.

Critical "Cannot Miss" Diagnoses

Pre-eclampsia

• Check blood pressure and proteinuria immediately 1
• Pre-eclampsia typically manifests after 20 weeks with new hypertension (≥140/90 mmHg) and new proteinuria
• Associated symptoms include headache, visual disturbances, epigastric pain, and vomiting 1
• Risk factors to assess: first pregnancy, age ≥40, BMI ≥35, multiple pregnancy, pre-existing hypertension/diabetes, family history 1
• This is your highest priority differential given the timing and symptom overlap

Neurological Emergencies

• Neurological disorders in pregnancy commonly present with headache, dizziness, nausea, and vomiting 2
• Consider:
  • Wernicke encephalopathy from thiamine deficiency (especially if prolonged vomiting) - presents with confusion, ataxia, oculomotor abnormalities 3
  • Intracranial pathology (hemorrhage, thrombosis, mass lesion)
  • Seizure disorder
• Perform neurological examination including Glasgow Coma Scale, cranial nerves, cerebellar function 2
• Lower Glasgow scores correlate with worse maternal outcomes 2

Common Pregnancy-Related Causes

Persistent/Recurrent NVP or Hyperemesis Gravidarum (HG)

• This is atypical timing - NVP resolves by 20 weeks in 90% of women 4
• Only 10% have symptoms persisting beyond 20 weeks
• HG defined by: severe nausea/vomiting starting before 16 weeks, inability to eat/drink normally, signs of dehydration, severely limiting daily activities 4
• Check for dehydration, electrolyte abnormalities (hyponatremia, hypokalemia), metabolic alkalosis 4
• Important caveat: Ketonuria does NOT indicate dehydration severity and should not guide management 4

Vestibular Disorders

• Pregnancy can exacerbate or trigger vestibular conditions 5, 6
• Consider:
  • Benign paroxysmal positional vertigo (BPPV) - positional vertigo with specific head movements
  • Vestibular migraine - episodic vertigo with migraine features
  • Ménière's disease - vertigo, tinnitus, hearing loss
  • Vestibular neuritis - acute prolonged vertigo
• Perform Dix-Hallpike maneuver, assess hearing, check for nystagmus 5, 7
• Hormonal changes affect inner ear structures during pregnancy 6

Rare but Serious Complications

Pulmonary Embolism

• HG patients are at increased risk for thromboembolism due to dehydration and immobility 8
• Presents with sudden dyspnea, chest pain, hemoptysis, tachycardia, tachypnea, dizziness 8
• Check oxygen saturation, heart rate, respiratory rate
• Pregnancy itself is prothrombotic; dehydration compounds this risk 8

Diagnostic Approach Algorithm

1. Immediate vital signs: Blood pressure, heart rate, respiratory rate, oxygen saturation, temperature

2. Focused examination:

   • Blood pressure for pre-eclampsia (≥140/90)
   • Neurological exam (Glasgow score, cranial nerves, cerebellar signs, mental status)
   • Signs of dehydration (mucous membranes, skin turgor, orthostatic changes)
   • Vestibular testing (nystagmus, Dix-Hallpike)
   • Respiratory assessment (tachypnea, chest pain)

3. Essential investigations:

   • Urine dipstick for proteinuria (pre-eclampsia)
   • Electrolytes, renal function, liver enzymes
   • Complete blood count (hematocrit elevation suggests dehydration)
   • Thyroid function (abnormal in 2/3 of HG cases) 4
   • Consider CT pulmonary angiography if PE suspected 8
   • MRI brain if neurological signs present 3

4. Risk stratification:

   • If hypertensive with proteinuria → pre-eclampsia pathway
   • If altered mental status/focal neurology → urgent neuroimaging
   • If respiratory distress → rule out PE
   • If positional vertigo → vestibular disorder
   • If isolated vomiting with dehydration → persistent NVP/HG

Critical Pitfalls to Avoid

• Do not dismiss symptoms as "normal pregnancy" at 20 weeks - NVP should have resolved 4
• Do not rely on ketonuria to assess severity 4
• Do not miss pre-eclampsia - it can present with vomiting and dizziness 1
• Consider thiamine supplementation if prolonged vomiting to prevent Wernicke encephalopathy 3
• Maintain high suspicion for PE in dehydrated pregnant patients despite prophylaxis 8