Background: In asthma, transitions between spirometric phenotypes following bronchodilator (BD) administration provide clinically relevant insights for pharmacological optimization. Objective: To evaluate prevalences of pre- to post-BD transitions by spirometric phenotypes and to investigate perinatal and current-life factors associated with transitions from pre-BD impaired phenotypes to post-BD normal spirometry. Methods: The study population comprised 44,394 patients with asthma aged 7–49 years who had at least one paired pre- and post-BD measurement of forced expiratory volume in 1 second (FEV1) and forced vital capacity, plus data on gestational age (GA) and birthweight. Patients were classified into spirometric phenotypes as follows: normal, PRISm (preserved ratio impaired spirometry), and airflow obstruction. Airflow obstruction was further categorized as dysanapsis, mild, moderate, or severe based on the FEV₁ z-score. Results: Normal lung function prevalence increased post-BD (Table 1), while other phenotypes decreased. Females had increased RRR of transitioning from dysanapsis or severe obstruction to normal lung function post-BD. Extremely-to-very preterm-born patients and those born small for GA (SGA) had decreased RRRs of transitioning from dysanapsis to normal lung function post-BD. Conclusions: Spirometric phenotypes shifted dynamically pre- to post-BD. Being born preterm or SGA was associated with a lower likelihood of transitioning from impaired to normal lung function. erj;68/suppl_70/PA5888/F1 F1 F1