Spirometry — Asthma in Pregnancy

A 28-year-old primigravida at 24 weeks gestation presents with worsening wheezing, nocturnal cough, and chest tightness 3–4 times per week requiring her rescue inhaler nightly. She has a history of childhood asthma and atopic dermatitis. On examination, bilateral expiratory wheezes and prolonged expiratory phase are noted. Pre-bronchodilator spirometry shows FEV₁ 68% predicted, FVC 88% predicted, and FEV₁/FVC ratio 0.62. After 4 puffs of inhaled albuterol via spacer, FEV₁ rises to 84% predicted—an increase of 380 mL and 23.5% from baseline. The flow-volume loop shows a scooped expiratory limb that improves toward normal after bronchodilator. The spirometric pattern marked **A** in the diagram is most consistent with which of the following diagnoses?