ABSTRACT Background Exposure definitions in real‐world pregnancy studies vary across studies, data sources, treatments and outcomes, yet their impact on prevalence estimates remains unexamined. Objectives To identify the most used exposure definitions during the 1st trimester and evaluate their impact on prevalence estimates: Methods We reviewed 400 randomly selected articles on medication use during pregnancy to identify exposure definitions. Using Danish health registers (1997–2024) and the Québec Pregnancy Cohort (1998–2015), we analysed chronic, as‐needed, and acute medication use. Prevalence (per 1000) was calculated per definition, including: (1) ≥ 1 or (2) ≥ 2 filled prescriptions during 1st trimester; filled ≥ 1 prescription anytime between the 1st trimester or (3) 30 days, (4) 60 days, (5) 90 days, (6) 6 months before conception; filled a prescription during 1st trimester or before conception, (7) assuming 1 daily defined dose per day or (8) prescribed days overlapping 1st trimester. Trends across cohorts and medications were compared. Results We analysed 1,524,075 pregnancies in Denmark and 229,000 in Québec, Canada. The most common exposure definitions identified from the literature were Definition 1 (83%), followed by Definition 3 (13%). Prevalence varied across definitions, with differential impacts depending on medication and type of use. Definition 6 (1st trimester or within the 6 months before conception) yielded the highest prevalence; Definition 2 (≥ 2 fills in 1st trimester) the lowest. Broader time‐windows of exposure increased prevalence, with variation by medication. The prevalence of medication use, whether chronic or acute, showed less variation across definitions than that of as‐needed medication. Conclusions Medication exposure prevalence varied by definition and medication. Using ≥ 1 filled prescriptions in the 1st trimester yielded prevalence estimates comparable to those from more complex definitions, supporting its use as a pragmatic standard. Sensitivity analyses and transparent reporting of exposure definition are essential to ensure replicability and critical appraisal.
Nohmie et al. (Fri,) studied this question.