The primary objective is to evaluate the Patent Ductus Arteriosus (PDA) closure rate of early vs. late use of Ibuprofen (Ibu). The investigators believe that early use of Ibu will have a higher PDA closure rate than later use of Ibu. Early use is defined as medication given before the infant reaches 96 hrs old. Late use is defined as medication given when infant is more than 96 hrs old.