The purpose of this trial is to study the effect that anemia and Red Blood Cell (RBC) transfusions have on oxygen levels in the digestive tracts of Extremely Low Birth Weight (ELBW) infants and to look for possible markers in a baby's blood, urine and/or stool that may lead to a better understanding of what makes an ELBW infant at risk for digestive tract problems such as necrotizing enterocolitis.