Postpartum depression affects some one in five new mothers, and adversely influences maternal adaptation to motherhood. While it is known that women with a prior history of depression, or depression during pregnancy, are at elevated risk for postpartum depression, many women with no prior history of depression or other risk factors go on to develop depression in the postpartum period. Considering the grave consequences of postpartum depression on maternal infant bonding and childhood psychological development, it is critical to develop reliable methods to identify which women, who are not depressed during pregnancy, will become depressed after delivery.