Legal abortion: limits and contributions to human life.

The traditional approach to abortion has been to regard it as disposing of human life, even when it is justifiable to induce abortion in accordance with legal and ethical principles. Contraception as distinct from abortion has never been so treated even though, in some respects, the biological processes involved in contraception and abortion raise similar issues. This is particularly so when contraception is by an intrauterine device or a postcoital technique which can prevent implantation rather than fertilization. Modern evidence shows that abortion is not only a loss of human life, but--paradoxically--is also a biological condition of human life. An unavoidably high rate of spontaneous loss of embryos has been shown to arise in the course of natural reproduction, due either to failure of implantation or to loss, such as the 'vanishing twin' of children born in single births. More common than the vanishing twin is spontaneous loss after implantation. Planned embryonic loss in artificial reproduction duplicates rather than defies nature. Further, sociological perceptions indicate that the availability of reliable prenatal diagnosis, especially of genetic conditions, and of induced abortion to terminate dysgenic life, may free couples to conceive and bear healthy children they would otherwise not have conceived. Moreover, prenatal diagnosis, for example by amniocentesis, may increasingly permit maternal or fetal treatment and so encourage the continuation of a pregnancy which might otherwise have been terminated.