Association between fetal hemoglobin level and the morbidity score. Figures show linear regression of (A) fetal hemoglobin level and (B) log fetal hemoglobin level against the morbidity score. Tables represent results of linear regression analysis after adjustment for indicated variables. NRBC indicates nucleated red blood cell; GDF, growth differentiation factor; NTBI, non–transferrin-bound iron; and CI, confidence interval.