Ethical issues in fetal surgery involving a twin pregnancy.

In utero surgery may provide benefit to a compromised fetus. The possibility of fetal surgery in a twin pregnancy extends the risk-benefit calculus beyond that of the fetus and mother to include the companion fetus and raises the issue of when, if ever, may fetus B be placed at substantial risk to benefit fetus A. Insight into the ethical dimensions of this issue is provided by the norms that govern the use of children in nontherapeutic research and the justifications used in twin-to-twin transplant cases.