For prospective parents, the customary one-or two-day wait to see fetal scans that might reveal abnormalities can seem interminable, but there are a couple of good reasons why it takes so long. The first problem is the fetuses: they wriggle, fidget, move, which makes it impossible to get a comprehensive and useful image. Radiologists solve that problem by scanning the fetuses “in slices” at different angles, then using computers to align the slices and create a three-dimensional image. That alignment, made possible with complex mathematical algorithms, is what takes so long.