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Flowchart of study cohorts. Cohort selection process for the three comparative cohorts: women who used macrolides during pregnancy versus those who used penicillin (that is, phenoxymethylpenicillin, main comparator); women who used macrolides during pregnancy versus those who used macrolides recently but before becoming pregnant; and women who used macrolides during pregnancy versus those who did not use any antibiotics (additional comparative groups) for the risk of major birth defects
