Scientific and religious controversies about the beginning of human life: the relevance of the ethical concept of the fetus as a patient.

In this paper we show that the question, "When does human life begin?", is not one question, but three. The first question is, "When does human biological life begin?", and is a scientific question. A brief review of embryology is provided to answer this question. The second question is, "When do obligations to protect human life begin?", and is a question of general theological and philosophical ethics. A brief review of major world religions and philosophy is provided to answer this question but has no settled answer and therefore involves irresolvable controversy. The third question is, "How should physicians respond to disagreement about when obligations to protect human life begin?" and is a question for professional medical ethics. A review of the ethical concept of the fetus as a patient is provided to answer this question. Physicians should manage the irresolvable controversy surrounding the second question by appealing to the ethical concept of the fetus as a patient. It is philosophically sound, respectful of all religious traditions and the personal convictions of patients and physicians alike, and clinically applicable.