Purpose <p>Certain women with heart disease require lifelong antithrombotic therapy. However, the impact of such therapy during pregnancy on maternal and neonatal outcomes remains unclear. This study aimed to investigate the prescription patterns and clinical outcomes associated with antithrombotic therapy in pregnant women with heart disease.</p> Methods <p>Using a Japanese administrative claims database, we identified pregnant women diagnosed with valvular heart disease or complex congenital heart disease between January 2008 and July 2023. In this retrospective observational study, we compared maternal clinical outcomes between women who were prescribed antithrombotic drugs during pregnancy and those who were not. For infants who could be linked to their mothers in the database, neonatal outcomes were also assessed.</p> Results <p>A total of 550 pregnant women with a history of heart disease were identified, of whom 90 (16.4%) received antithrombotic therapy during pregnancy. Women who received antithrombotic therapy had a higher proportion of cesarean delivery (90.0% vs. 49.8%, <i>p</i> &lt; 0.001). Intensive care unit (ICU) admission rate was significantly higher in this group (24.4% vs. 10.5%, <i>p</i> &lt; 0.001), as was critical obstetric bleeding (13.3% vs. 1.7%, <i>p</i> = 0.009). No in-hospital maternal deaths or fatal arrhythmias were observed. Among the neonates associated with their mothers, a total of 238 were identified. Admission to a neonatal ICU was significantly more frequent among infants born to women who received antithrombotic therapy (35.7% vs. 13.3%, <i>p</i> = 0.001).</p> Conclusion <p>Although careful maternal and neonatal management is necessary, no in-hospital maternal deaths or severe cardiovascular events were observed among women prescribed antithrombotic therapy. This study provides valuable evidence to inform clinical decision-making in pregnant women with valvular heart disease requiring antithrombotic therapy in Japan.</p>