Abstract: Described are methods for treating, preventing, or reducing the risk of, miscarriages, especially recurrent miscarriages. The methods comprise administering to a female subject a therapeutic agent that modulates the activity or binding of components of the complement system, together with a pharmaceutically acceptable carrier. For example, the therapeutic agent can be a C3-convertase inhibitor, an antibody against C5, an antagonist of the C5a receptor, or an antibody against factor B or factor D. Screening methods for agents that can prevent or reduce the risk of miscarriages, especially recurrent miscarriages, are also described.