Main findings
In this prospective cohort study, we did not observe decreased risks of late-onset preeclampsia after use of calcium-based antacids or PPIs during pregnancy, irrespective of the timing of use. In contrast, low dose calcium-based antacid use in gestational weeks 0-16 and any PPI use in gestational weeks 17-33 were associated with a modestly increased risk of late-onset preeclampsia.