Birth control is a regimen of one or more actions, devices, sexual practices, or medications followed in order to deliberately prevent or reduce the likelihood of pregnancy or childbirth. There are three main routes to preventing or ending pregnancy before birth: the prevention of fertilization of the ovum by sperm cells ("contraception"), the prevention of implantation of the blastocyst ("contragestion"), and the chemical or surgical induction or abortion of the developing embryo or, later, fetus. In common usage, term "contraception" is often used for both contraception and contragestion.