This is a population-based two-stage cohort study that will take advantage of a new KPNC region-wide program of peripartum screening for depression which annually screens about 33,000 pregnant women for depression twice during pregnancy and once post-partum. The study will specifically determine: 1) What is the risk of preterm delivery and postpartume depression (PPD) among women who screen positive for depression during pregnancy compared to those who screen negative for depression. 2. What is the effect of three treatment regimens for depression (i.e., group and individual therapies, and pharmacological treatment) on reducing the risk of preterm delivery and PPD. 3) Which treatment is most effective in reducing the risk of preterm delivery and PPD. 4) Is the effectiveness of the treatment related to timing, dose, and duration of the treatment.