By: Cynthia Rhymes E-mail: CRhymes@hotmail.com December 21, 1999 The Hope, and Hype, of Cord Blood By DENISE GRADY Should parents pay a blood bank to store the blood from their newborn baby's umbilical cord and placenta, in case that child or another family member ever needs it to treat cancer or leukemia? Expectant parents are being urged to do so by companies that have sprung up during the past few years to sell cord-blood banking as a form of "biological insurance" against such dreaded diseases. The pitch is based on reports in medical journals, such as a major study published last week in the New England Journal of Medic