In this study, the investigators believe that the use of both prevention strategies will result in a lower rate of TT-CMV, and that the "cause" of TT-CMV may be found in the presence of CMV at the DNA level or by unfiltered white cells that remain in the blood product. Thus, the most significant clinical question that remains to be addressed is whether this double strategy for transfusion safety actually provides a "zero CMV-risk" blood supply or whether further safety measures (DNA testing + 100% leukoreduction) must be used to protect this extremely vulnerable patient group from CMV infection. This birth cohort study will be done with 6 participating NICUs, and will study both CMV positive and negative mothers in order to estimate the rate and pathway of CMV transmission to the LBWI who receives a transfusion. Another study goal is to compare or link any CMV infection by either transfused units where the virus was undetected, or filter failure. If CMV disease occurs, the investigators will be able to describe the course and outcome in LBWIs who develop TT-CMV.