The 20-week marker is one of the most important milestones of a pregnancy. For most expectant mothers, the ultrasound that is usually first performed then is their first chance to see what their baby looks like. Hands and feet are identified. Those familiar black-and-white photographs are printed out and shown to friends and family. Everything suddenly feels more real.For Kate Cox, a 31-year-old woman who lives in Dallas, the 20-week milestone turned into a nightmare. Her doctors told her that t