A new study has uncovered how stress experienced by mothers during pregnancy leaves a molecular imprint on their babies—starting before birth. The research shows that prenatal stress alters the expression of tiny RNA molecules in newborn blood, particularly in female children, and affects key enzymes in the brain's stress-regulation system. These changes may help explain why some children are more vulnerable to developmental or psychiatric challenges. The study opens new possibilities for early diagnosis and interventions targeting stress-related health risks.