Stress and anxiety during pregnancy predict perinatal complications over the course of pregnancy and labor as well as premature birth and low infant birth weight. The current study examined whether relaxation training provided to women at the beginning of the 2nd trimester could reduce stress and anxiety and assessed the impact of the intervention on perinatal complications, premature delivery, and infant outcomes at birth. Twenty-six moderately anxious pregnant women between 14 and 20 weeks gestation participated in the treatment study. Women completed a baseline laboratory assessment that involved questionnaires and a psychophysiological assessment. They were randomized to receive either six weeks of relaxation training or a list of tips for reducing stress (control). Women repeated the laboratory tasks post-treatment (Time 2) and again between 34 and 36 weeks gestation (Time 3). The treatment condition did not lead to greater mood change than the control condition at either Time 2 or 3. Several analyses, however, suggest relaxation training has the potential for reducing negative mood and complications over the course of pregnancy. Moderator analyses also revealed the treatment more efficacious for those with greater physiological flexibility.