The day after her first child was born in January at Virginia Hospital Center in Arlington County, Suzanne Libby discovered that he was missing from the hospital nursery. Searching frantically, she found Spencer in his hospital bassinet -- in another woman's room. Standing next to him was a hospital aide, a stricken look on her face. The relief that Libby felt at finding her son was later replaced by fresh anxiety: The woman, it turned out, had breast-fed her newborn. More than two hours passed before hospital officials told Libby, 34, and her husband, Reed, 36, how the mix-up had happened: The aide had neglected to match Spencer's ID bands with the other woman's. The next day, hospital officials told the couple that results of blood tests run on the woman showed she did not have HIV or hepatitis B or C, diseases that can be passed to a baby through breast milk.