Medication use trajectories in myasthenia gravis pregnancies: a population-based drug utilization study.

OBJECTIVE: To examine medication use trajectories from 1 year before pregnancy to 6 months postpartum in a population-based birth cohort of patients with myasthenia gravis (MG). METHODS: We used harmonized and pooled national register data from Norway and Sweden (1994-2023) to identify MG pregnancies. Longitudinal dispensing records of symptomatic MG medications, oral corticosteroids (OCS), and non-steroidal immunosuppressant therapy (NSIST) were extracted from prescription registers, which were individually linked to hospital records in the national patient registers and demographic and clinical data in the medical birth registers. Group-based multi-trajectory modeling (GBMTM) was used to identify pregnancy clusters and typical mono- or polytherapy medication use trajectories until delivery. RESULTS: Among 339 MG pregnancies, 201 (59%) used some MG medication during pregnancy or 1 year before. Four distinct multi-drug trajectories were identified: 'Intermittent users,' 'Persistent symptomatic-only users,' 'Immunosuppressant plus symptomatic users,' and 'Immunosuppressant-only users.' Most symptomatic medication users remained on a stable medication use trajectory during pregnancy. Increased use of OCS was overall rare, but occurred in around 10% of "Intermittent users". 'Immunosuppressant-only users' had stable OCS use throughout the study period and frequent non-MG hospital contacts, but rarely contacts due to MG. Although MG-related admissions were infrequent overall, they were consistently higher among 'Immunosuppressant plus symptomatic users'. Further, 'Immunosuppressant plus symptomatic users' often discontinued NSIST during pregnancy. INTERPRETATION: Most patients had no, low, or stable medication use throughout pre-pregnancy and pregnancy. Medication use trajectories discriminated MG patients with similar phenotypes and distinct healthcare utilization patterns. Such subgroups likely represent distinct disease courses in relation to pregnancy which could help in the development of individualized care pathways.