Analysis of over 5 million American two‑child families finds firstborns face higher neurodevelopmental and allergy risks, while second‑borns show greater odds of substance use, gastrointestinal and infection‑related conditions.
Analysis of over 5 million American two‑child families finds firstborns face higher neurodevelopmental and allergy risks, while second‑borns show greater odds of substance use, gastrointestinal and infection‑related conditions.