A full-term male infant was born to a 33-year-old gravida 3, para 3 mother. The prenatal course was uncomplicated, without gestational diabetes; the mother received prenatal care at an out-of-state institution. At the delivery, however, the baby was notably macrosomic, with shoulder dystocia and perinatal distress requiring positive pressure ventilation.
The infant’s APGAR scores were 2 and 8 at 1 and 5 minutes, respectively. Birth anthropometrics showed a weight of 4385 grams (>97th percentile); a birth length of 58.5 cm (>97th percentile); and a head circumference of 37.5 cm (~75th percentile). Physical examination was otherwise unremarkable.
The baby’s initial point-of-care glucose value, obtained from a heel stick sample, at 2 hours of life was 22 mg/dL, with a confirmatory serum glucose of 37 mg/dL. He had no concerning symptoms such as seizures, lethargy, or poor feeding. Despite regular formula feeds, the serum glucose remained in the 40-mg/dL to 49-mg/dL range. An intravenous (IV) dextrose infusion was started with a glucose infusion rate (GIR) of 9 mg/kg/min. At this time, it was presumed that the hypoglycemia was transient, a result of the macrosomia combined with perinatal stress. The baby was evaluated for 48 hours for sepsis; his blood culture ultimately was negative.
Over the next 3 days, the dextrose concentration in the patient’s IV fluids was increased. By the third day of life, he was maintained on a GIR of 17 mg/kg/min to keep his serum blood sugar above 60 mg/dL. The differential diagnosis at this time expanded to include: hypopituitarism, adrenal insufficiency, growth hormone deficiency, inborn errors of metabolism, and congenital hyperinsulinism.1 A critical serum sample drawn during a hypoglycemic event of 32 mg/dL on point-of-care testing demonstrated the following: serum glucose, 41 mg/dL; cortisol, 17.6 μg/dL (normal during hypoglycemia, >17 ug/dL); growth hormone, 30.6 ng/mL (normal during hypoglycemia, >8.8 ng/mL); undetectable plasma ketones (fasting normal, 0.2-2.8 mg/dL); undetectable free fatty acids (fasting normal, 0.43-1.37 mmol/L); and insulin, 61 μU/mL (normal during hypoglycemia, <2 μU/mL).