A study published Monday finds that stressful pregnancies actually reduce the chances of having a boy. Researchers found that pregnant women who exhibited higher blood pressure and other signs of stress had four boys for every nine girls, while moms who weren't as stressed had two boys for every three girls. "The womb is an influential first home. We do know that males are more vulnerable in utero, and presumably the stress in these women is of a long-standing nature," says lead study author Catherine Monk. "Other researchers have seen this pattern of a decrease in male births related to traumatic cataclysmic events, one of them being President Kennedy's assassination and the other being the September 11 terrorist attacks in New York City."