Hypothesized causal relation between the postnatal rate of rise of total serum bilirubin, associated risk factors, as well as timing and duration of phototherapy in very low birth weight preterm infants.1 a) Aspects of bilirubin metabolism in physically immature infants.2 BW, birth weight; GA, gestational age; RBC, red blood cell; RS, Spearman’s rank coefficient; TSB, total serum bilirubin; TSB ROR, rate of rise of total serum bilirubin (mg/dL/h).