Inhaled Corticosteroids Continuation in the First Trimester and Pregnancy Outcomes in Women With Asthma.

Importance: Asthma control during pregnancy is critical to prevent maternal and perinatal complications. Although guidelines recommend continuing inhaled corticosteroids (ICSs), discontinuation is common and clinical evidence of major maternal and neonatal outcomes limited. Objective: To evaluate the association between ICS continuation during the first trimester of pregnancy and maternal and neonatal outcomes. Design, Setting, and Participants: This nationwide, population-based cohort study used a mother-child linked health care database (January 1, 2009, to December 31, 2023) and included live births in Korea between April 1, 2010, and December 31, 2022. Women (aged 15-50 years) with asthma who received at least 2 ICS prescriptions in the 6 months before their last menstrual period were identified to increase the likelihood that prescription records reflected ongoing ICS use. Data were analyzed from April 28 to November 10, 2025. Exposure: Women classified as ICS continuers (≥1 ICS prescription during the first trimester) or discontinuers (no prescription during the same period). Main Outcomes and Measures: Maternal outcomes included preeclampsia, gestational diabetes, obstructed labor, antepartum hemorrhage, premature rupture of membranes, and preterm birth; neonatal outcomes included hypoxia or asphyxia, low birth weight, and congenital malformations. Propensity score overlap-weighted log-binomial regression models were used to estimate risk ratios (RRs) and 95% CIs for each maternal and neonatal outcome. Results: Among 3 909 084 pregnancies, 6105 involved prepregnancy ICS use for asthma. A total of 2108 women (34.5%; mean [SD] age, 33.2 [4.4] years) continued ICS in the first trimester, and 3997 women (65.5%; mean [SD] age, 32.9 [4.2] years) discontinued use. Risks per 1000 pregnancies for ICS continuation vs discontinuation, respectively, were as follows: gestational diabetes, 145.6 vs 131.9 (weighted RR, 1.05; 95% CI, 0.90-1.22); preterm birth, 131.4 vs 128.6 (weighted RR, 0.95; 95% CI, 0.82-1.11); low birth weight, 77.5 vs 58.3 (weighted RR, 1.11; 95% CI, 0.89-1.39); and congenital malformations, 57.6 vs 42.2 (weighted RR, 1.22; 95% CI, 0.94-1.56). Continuation of ICSs was not associated with increased risks of these or other maternal and neonatal outcomes. Conclusions and Relevance: This nationwide cohort study found that continued ICS use during early pregnancy was not associated with increased risks of maternal or neonatal outcomes, despite frequent discontinuation. These findings provide reassuring evidence supporting current guideline recommendations to continue ICS therapy during pregnancy and highlight the importance of individualized risk assessment while maintaining asthma control.