A female infant weighing 2,730 g is born at 37+4 weeks of gestation by elective cesarean delivery to a multigravida mother. This is the mother's fifth pregnancy. She has had 3 abortions and an undiagnosed neonatal death at 30 days. The infant who died suffered unexplained neonatal jaundice and received an exchange transfusion at 10 days of age. Because of poor obstetric history and death of the last infant, the parents were very apprehensive. This infant developed jaundice on day 1 of age. Because of her total serum bilirubin (SBR) of 5.4 mg/dL (92.3 μmol/L) at 15 hours and 9.6 mg/dL (164.1 μmol/L) at 24 hours of age, she was referred to the authors’ practice. On arrival, at 2 days of age, she had jaundice, with a heart rate of 120 beats per minute, respiratory rate of 65 breaths per minute, oxygen saturation of 95% in room air, and a capillary refill of less than 3 seconds. Systemic examination findings were unremarkable. A diagnosis of neonatal jaundice was made and phototherapy commenced. Her complete blood cell (CBC) count revealed the following: hemoglobin, 15.5 g/dL (155 g/L); white blood cells (WBC), 12,100/μL (12.1 × 109); platelets, 336 × 103/μL (336 × 109/L); SBR, 13.3 mg/dL (229 μmol/L) at 48 hours of age (just above the phototherapy threshold line); blood group, O positive (mother's blood group, B negative); reticulocyte count, 1.2%; and direct and indirect Coombs test, negative. A prefeeding blood glucose concentration was 98 mg/dL (5.4 mmol/L). Though the mother had had anti-D in the past, a presumed diagnosis of blood group incompatibility was considered because the infant’s jaundice had appeared in the first 24 hours of age. On day …