What is the most likely diagnosis and recommended next steps for a 25‑year‑old woman at 26 weeks gestation presenting with a one‑day history of a dull frontal headache and low‑grade fever that improved with acetaminophen, with chronic hypotension but otherwise normal examination?

Likely Diagnosis and Next Steps for 25-Year-Old Pregnant Woman with Headache and Fever

Most Likely Diagnosis

This presentation is most consistent with a self-limited viral illness or tension-type headache that has already resolved, but you must rule out early preeclampsia and other secondary causes before reassuring the patient. 1, 2

The key clinical features pointing toward a benign primary process include:

• Complete symptom resolution by time of consultation 1
• Dull, non-pulsating frontal headache without neurological symptoms 1
• Low-grade fever (38.5°C) that responded to acetaminophen 3
• Normal physical examination except chronic hypotension 1
• Environmental trigger (cold office) 1

However, 35% of pregnant women presenting with acute headache have secondary causes, with hypertensive disorders being the most common (51% of secondary headaches). 1, 2

Critical Red-Flag Assessment

Features PRESENT That Warrant Concern

• Lack of documented headache history – This is the single strongest predictor of secondary headache in pregnancy (OR 4.9), present in 36.7% of secondary vs. 13.2% of primary headaches 1, 2
• Third trimester presentation (26 weeks AOG) – Secondary causes increase in frequency as pregnancy advances 2, 4
• Fever – Associated with secondary headache (8.2% vs. 0% in primary, p=0.014) 1, 2

Reassuring Features ABSENT

• No elevated blood pressure (BP 90/70 mmHg) – Elevated BP is the strongest predictor of secondary headache (OR 17.0) 1, 2
• No seizures 1
• No abnormal neurological examination 1
• No proteinuria documented 2

Immediate Next Steps

1. Obtain Baseline Blood Pressure and Proteinuria Assessment

Blood Pressure Measurement:

• Confirm BP with repeat measurement using proper technique 3, 5
• Document that BP remains <140/90 mmHg (threshold for hypertension in pregnancy) 3, 5, 6
• Her chronic hypotension (90/70 mmHg) is reassuring but does not exclude preeclampsia, which is defined by new-onset hypertension ≥140/90 mmHg after 20 weeks 3

Proteinuria Screening:

• Perform automated dipstick urinalysis 5
• If positive (≥1+), obtain spot urine protein-to-creatinine ratio or 24-hour urine collection 5
• Significant proteinuria is ≥0.3 g/24h or ≥30 mg/mmol creatinine 3, 5

2. Laboratory Evaluation

Order the following to screen for preeclampsia and other secondary causes:

• Complete blood count (CBC) – to assess for thrombocytopenia (platelets <100,000), which occurs in HELLP syndrome 3, 2
• Liver function tests (AST, ALT) – elevated in preeclampsia/HELLP 3, 2
• Serum creatinine – to assess renal function 3
• C-reactive protein (CRP) – elevated CRP is a red flag for secondary headache 2

3. Detailed Headache History

Specifically document:

• Any prior headache history – absence increases secondary headache risk 4.9-fold 1, 2
• Duration of current episode (resolved <24 hours is reassuring) 1
• Presence of migraine features: photophobia, phonophobia, nausea, pulsating quality 1, 4
• Any change from prior headache pattern 2, 4

4. Fetal Assessment

• Perform non-stress test or biophysical profile to assess fetal well-being 3
• Document fetal movement 3

Disposition and Follow-Up

If All Workup is Normal:

• Diagnosis: Likely primary headache (tension-type or migraine) or self-limited viral illness 1, 4
• Acute treatment: Acetaminophen 1000 mg is safe and appropriate for mild-to-moderate headache in pregnancy 3, 7, 8
  • Maximum dose: 4000 mg/24 hours 8
  • Limit use to ≤2 days per week to prevent medication-overuse headache 7
• Return precautions: Instruct patient to return immediately for:
  • Severe headache ("worst headache of life") 2, 4
  • Visual changes or neurological symptoms 3, 2
  • Elevated blood pressure ≥140/90 mmHg 3, 5, 6
  • Persistent fever >38°C 1, 2
  • Decreased fetal movement 3
• Follow-up: Routine prenatal visit within 1 week to recheck BP and review labs 3, 5

If Any Abnormalities Are Found:

• Elevated BP ≥140/90 mmHg: Diagnose gestational hypertension; monitor closely for progression to preeclampsia 3, 5
• Proteinuria + hypertension: Diagnose preeclampsia; consider hospital admission for monitoring 3
• Severe hypertension ≥160/110 mmHg: Immediate treatment required within 15 minutes with IV labetalol, hydralazine, or oral nifedipine 3, 6
• Thrombocytopenia or elevated liver enzymes: Evaluate for HELLP syndrome; urgent obstetric consultation 3, 2

Neuroimaging Indications

Do NOT obtain neuroimaging if all of the following are true:

• Normal neurological examination 1, 9
• No red-flag features (thunderclap onset, progressive worsening, focal deficits) 2, 9, 4
• Symptoms have resolved 1
• Normal BP and labs 1, 2

Obtain MRI brain (preferred over CT to avoid radiation) if any of the following are present:

• Abnormal neurological examination 1, 9
• Persistent or worsening headache despite treatment 9, 4
• Atypical features (thunderclap onset, change in pattern) 2, 9
• Elevated BP with severe headache (to rule out posterior reversible encephalopathy syndrome [PRES]) 9, 4

Key Pitfalls to Avoid

1. Do not dismiss headache solely because BP is normal – Preeclampsia can develop rapidly, and this patient is at 26 weeks (after the 20-week threshold) 3, 5
2. Do not assume primary headache without documenting prior headache history – Lack of headache history is the second-strongest predictor of secondary causes 1, 2
3. Do not prescribe NSAIDs (ibuprofen, naproxen) after 20 weeks gestation – Risk of premature ductus arteriosus closure 7
4. Do not use opioids for headache in pregnancy – Limited efficacy, high dependence risk, and rebound headache 7
5. Do not delay workup for preeclampsia – Hypertensive disorders account for 51% of secondary headaches in pregnancy and are a leading cause of maternal mortality 3, 1, 2