In a 28‑week pregnant woman presenting with cough, dyspnea, bilateral rhonchi, and a history of allergy, what is the most appropriate initial investigation?

Most Appropriate Initial Test for 28-Week Pregnant Woman with Cough, Dyspnea, Bilateral Rhonchi, and Allergy History

The most appropriate initial test is spirometry (Option A), as it is the preferred objective method for assessing lung function in pregnant women with suspected asthma and is safe, non-invasive, and provides essential diagnostic information without radiation exposure.

Clinical Context and Diagnostic Approach

This presentation strongly suggests asthma exacerbation or new-onset asthma in pregnancy, given the combination of:

• Respiratory symptoms (cough, dyspnea) with bilateral rhonchi 1
• History of allergy (a key risk factor for atopic asthma) 1
• Second/third trimester timing (when asthma symptoms commonly worsen) 1

Why Spirometry is the Optimal Initial Test

Spirometry is specifically recommended as the preferred diagnostic tool for pregnant women with suspected asthma 1. The key advantages include:

• No radiation exposure to mother or fetus, making it completely safe in pregnancy 1
• Objective assessment of airway obstruction through FEV1/FVC ratio measurement 2, 3
• Documentation of reversibility when performed with bronchodilator testing, which is essential for confirming asthma 2, 3
• Superior to peak flow measurement for initial diagnosis, though peak flow can be used for ongoing monitoring 1
• Well-tolerated in pregnancy with high patient satisfaction scores (4.75 ± 0.72) across all trimesters 4

Why Other Options Are Less Appropriate

Chest X-ray (Option B) should be reserved for specific indications:

• While chest radiography has value in evaluating suspected pulmonary embolism in pregnancy 5, this patient's presentation (bilateral rhonchi, allergy history, no mention of pleuritic chest pain or risk factors for PE) is more consistent with asthma
• Involves unnecessary radiation exposure when a non-radiation alternative (spirometry) provides more diagnostic information for the suspected condition 1

ABG (Option C) is not an initial test because:

• Reserved for severe exacerbations requiring assessment of oxygenation and ventilation status 6
• This patient's presentation doesn't suggest severe respiratory failure requiring immediate ABG
• Spirometry provides more specific diagnostic information for asthma 1, 2

Hemoglobin estimation (Option D) is not relevant to this acute respiratory presentation and would not help diagnose the underlying cause of cough and dyspnea.

Critical Management Considerations After Spirometry

Once spirometry confirms airway obstruction:

• Initiate or optimize controller therapy immediately with inhaled corticosteroids (budesonide preferred in pregnancy due to extensive safety data) 6, 1
• Assess for reversibility with bronchodilator testing (albuterol 2.5-5 mg via nebulizer) 6, 2
• Never withhold asthma medications due to pregnancy concerns, as uncontrolled asthma poses far greater risks (preterm birth, low birthweight, preeclampsia, perinatal mortality) than any medication 6, 1
• Maintain oxygen saturation >95% to ensure adequate fetal oxygenation 6

Common Pitfalls to Avoid

• Do not delay objective testing by relying solely on clinical examination, as spirometry is essential for confirming the diagnosis 1, 2
• Do not order chest X-ray first when clinical presentation suggests asthma rather than pneumonia or PE, as this exposes the fetus to unnecessary radiation 1
• Do not assume normal pregnancy dyspnea without objective testing, as one-third of pregnant women experience worsening asthma 1
• Consider GERD as a comorbid trigger, as it commonly exacerbates asthma in pregnancy and should be addressed concurrently 6