A child's disposition has long been linked--fairly or not--to his or her mother's emotional state during pregnancy. Recent research lends some credibility to that belief. A study of 70 mothers found that women with high anxiety levels from weeks 12 to 22 of their pregnancies were more likely to have children who act out or are hyperactive as 8-and 9-year-olds. While maternal stress can trigger physiological events that might affect fetal development, the exact mechanism is not clear. Also uncertain is whether the anxious moms were themselves genetically predisposed to hyperactivity. Researchers hope that timely intervention might benefit both anxious mothers-to-be and their kids.