Research to improve the health of pregnant and fetal patients presents ethical challenges to clinical investigators, institutional review boards, funding agencies, and data safety and monitoring boards. The Common Rule sets out requirements that such research must satisfy but no ethical framework to guide their application. We provide such an ethical framework, based on the ethical concept of the fetus as a patient. We offer criteria for innovation and for Phase I and II and then for Phase III clinical trials to improve the health of pregnant patients and of fetal patients and also criteria to responsibly manage the transition from investigation to clinical practice. Basing ethical criteria for research involving pregnant women on the ethical concept of the fetus as a patient insulates the proposed ethical framework and therefore research on pregnant women from the divisive and politicized concepts and discourses of personhood, fetal rights, and unborn child.