Key Takeaways: Children with both a low 5-minute Apgar score and low umbilical cord blood pH at birth had a greater risk of developing ADHD than reference newborns. No increased ADHD risk was observed when Apgar score or umbilical cord pH was low in isolation. The findings suggest combined clinical and biochemical indicators of perinatal hypoxia may better identify ADHD risk while offering reassurance to families when only 1 marker is abnormal.