In a 29-year-old woman with four days of persistent nausea after a brief headache, mild pharyngeal irritation, transient urinary frequency, and a recent menstrual period, what is the most likely diagnosis, which investigations are indicated, and is anti‑emetic therapy appropriate?

Clinical Assessment and Management

This presentation most likely represents early pregnancy with nausea and vomiting of pregnancy (NVP), and you should immediately obtain a urine or serum pregnancy test before pursuing other investigations or initiating anti-emetic therapy.

Most Likely Diagnosis

The clinical picture strongly suggests early pregnancy:

• The constellation of persistent nausea following headache, recent menstrual period, and transient urinary frequency (which has now resolved) is classic for early pregnancy 1
• Nausea and vomiting typically peak at 8-12 weeks gestation and can begin shortly after conception, often presenting as the primary symptom before a missed period is recognized 1
• The initial headache followed by nausea could represent hormonal fluctuation effects, as menstrual-related migraine affects 20-25% of women and is triggered by estrogen withdrawal around menstruation 2
• Urinary frequency is an early pregnancy symptom that can occur before a missed period due to hormonal changes

Essential Investigations

First-line investigation:

• Urine pregnancy test (or serum β-hCG if urine test unavailable) - This is the single most important test and must be done before any other workup or treatment 1

If pregnancy test is positive:

• Assess severity using the PUQE (Pregnancy-Unique Quantification of Emesis) score: mild (≤6), moderate (7-12), severe (≥13) 1
• Check for signs of hyperemesis gravidarum: dehydration, weight loss >5% of prepregnancy weight, electrolyte abnormalities 1
• Basic metabolic panel if moderate-to-severe symptoms or signs of dehydration 1

If pregnancy test is negative:

• Throat swab for Group A Streptococcus given pharyngeal symptoms
• Urinalysis and urine culture (despite resolution of urinary symptoms, subclinical UTI can cause nausea)
• Consider viral pharyngitis workup given the throat irritation and systemic symptoms

Anti-Emetic Therapy Appropriateness

Yes, anti-emetic therapy is appropriate, but the choice depends critically on pregnancy status:

If pregnant (most likely scenario):

• Start with vitamin B6 (pyridoxine) 10-25 mg every 8 hours as first-line therapy 1
• Add doxylamine if B6 alone is insufficient 1
• For moderate symptoms not responding to first-line: consider H1-receptor antagonists (promethazine, dimenhydrinate), metoclopramide, or ondansetron 1
• Metoclopramide has similar efficacy to promethazine with fewer side effects 1
• Dietary modifications: small, frequent, bland meals; BRAT diet; high-protein, low-fat meals 1

If not pregnant:

• Standard anti-emetics (ondansetron, metoclopramide, promethazine) are appropriate
• Treat underlying cause (pharyngitis, UTI, viral illness)

Critical Pitfalls to Avoid

• Never prescribe anti-emetics without first confirming pregnancy status - pregnancy-safe options must be prioritized if she is pregnant 1
• Do not dismiss the urinary frequency as irrelevant even though it has resolved - it supports early pregnancy as the diagnosis
• Early intervention is crucial to prevent progression to hyperemesis gravidarum 1
• The negative malaria test helps rule out infectious causes but does not exclude pregnancy

Algorithmic Approach

1. Obtain pregnancy test immediately
2. If positive: Calculate PUQE score → Start B6 ± doxylamine → Escalate to other anti-emetics if needed → Monitor for hyperemesis gravidarum
3. If negative: Investigate pharyngitis and UTI → Treat underlying cause → Use standard anti-emetics as needed