Anticoagulant therapy has been used extensively for the prevention of recurrent pregnancy losses, and other placenta mediated complications, including prevention of preeclampsia and fetal growth restriction. While heparin anticoagulation is a standard treatment for antiphospholipid antibody syndrome, it is increasingly being used in the prevention of placenta mediated complications. In this article, we explore the role of heparin at maternal-fetal interface, the molecular mechanism of action for heparin, and ongoing basic and translational work being done to elucidate heparin's principal mechanisms of action.