Which of the following conditions can hypoxic spells in infants with congenital heart defects lead to?

Hypoxic spells in infants with congenital heart defects can lead to polycythemia because these spells cause a decrease in oxygen levels in the blood. When the body senses low oxygen levels, it responds by increasing the production of red blood cells to enhance the blood's oxygen-carrying capacity. This compensatory mechanism is known as erythropoiesis. The increased red blood cell production can result in polycythemia, which is characterized by an elevated hematocrit and hemoglobin concentration.

The other conditions listed are not directly related to hypoxic spells. Diabetes and obesity are metabolic conditions that are not influenced by hypoxia in the same immediate manner, while asthma is primarily a respiratory condition characterized by airway inflammation and obstruction rather than a direct consequence of hypoxic spells related to congenital heart defects. Therefore, the production of excess red blood cells due to low oxygen levels is what links hypoxic spells to the development of polycythemia in these infants.