What is it about terminating half a twin pregnancy that seems more controversial than reducing triplets to twins or aborting a single fetus? After all, the math’s the same either way: one fewer fetus. Perhaps it’s because twin reduction (unlike abortion) involves selecting one fetus over another, when either one is equally wanted. Perhaps it’s our culture’s idealized notion of twins as lifelong soul mates, two halves of one whole. Or perhaps it’s because the desire for more choices conflicts with our discomfort about meddling with ever more aspects of reproduction.