Roe v. Wade (1973)
In this now threatened landmark case, the Supreme Court ruled unconstitutional a state law that made abortion a criminal offense on the grounds that it violated the due process clause of the Fourteenth Amendment which protected the right of privacy.  The right of privacy included the qualified right to terminate a pregnancy, depending on the stage of pregnancy involved.  After six months of a pregnancy, the state has the right to restrict abortion except where necessary to preserve the life of the mother.   

http://www.oyez.org/cases/1970-1979/1971/1971_70_18/