A baby's immune system may be suppressed if its mother is stressed during pregnancy, according to a study by researchers at the University of Rochester Medical Center. The response was most pronounced in 6-month-old babies who had not yet received their third vaccinations. After the third dose, however, the stress effects from the mother disappeared. "The key issue that various folks are struggling with is to find out if interventions in pregnancy can reduce the effects. We just don't know the answer to that yet," said researcher Tom O'Connor.