Serum was separated from blood samples. After all study assays were completed on all subjects, if a subject's parents asked that his/her serum not be stored, the serum was destroyed. For subjects whose parents permit it, leftover serum was re-labeled with a new, randomly-generated unique de-identifier, linked only to the subject's gestational age, birth weight, and chronologic age at the time of sampling. The link to any other subject identifiers will then be destroyed. The serum will be stored indefinitely at the University of Rochester for other, non-genetic-testing-related research.