PROJECT SUMMARY/ABSTRACT Perinatal depression poses a potential long-term negative health impact on the mother and the fetus due to treatments with SSRI. Very little basic research is available on the use of medications during pregnancy and lactation on the effects of pregnancy maintenance, fetal development, and mammary gland development. Antidepressant use during pregnancy has been shown to increase risks of preterm birth, birth defects, and pulmonary hypertension in newborns. Our research has discovered that use of SSRI during pregnancy has resulted in increased early pregnancy loss in dams. Furthermore, we have observed increased pup mortality in the first two days post-partum. To this end, we have observed underdevelopment of the mammary gland, indicating this could possibly due to the inability to lactate. The continuation of SSRI use in depressed women is critical to maternal health. Therefore, it is critical to understand the underlying contributions of SSRI to early pregnancy loss and increased pup mortality postpartum. SSRI's are the preferred method of treatment of maternal depression. It is critical to determine the mechanisms underlying early pregnancy loss and increased early postpartum mortality. This will allow for support to be provided to women who are pregnant, or attempting to achieve pregnancy, while being treated for depression with SSRIs. Furthermore, this research will be critical for understanding the contribution of SSRIs to issues related to the development of the fetus and this will provide critical information for neonatologists to support infants born to women using SSRIs for the treatment of depression. Additionally, determination of the effects of SSRI on mammary gland development will be critical to supporting women who want to breastfeed and are being treated for maternal depression. The effects of SSRI on pregnancy, fetal development, and mammary gland development is a grossly understudied area. It is critical to delineate the mechanisms contributing to these issues to better provide support to women who are being treated for depression during the perinatal period.