A 2-day-old full-term Indian newborn is brought to the clinic by anxious parents who report that the baby's hands and feet appear bluish, particularly when the baby is cold. On examination, the structure marked **A** in the diagram (pink tongue and mucous membranes) is clearly visible with no discoloration. The trunk is pink, capillary refill is less than 3 seconds, and the infant is feeding well with normal oxygen saturation on room air. Which of the following is the most appropriate next step in management?