Temperature instability in a newborn could result from:

Rationale: A. Hypoxia may cause some stress responses but is not the most common cause of temperature instability in a newborn. B. Congenital heart disease can affect perfusion but typically does not directly cause temperature instability. C. Polycythemia may affect circulation but is not a primary cause of abnormal temperature regulation. D. Sepsis is a common cause of temperature instability in newborns, manifesting as hypothermia or hyperthermia. Newborns have immature thermoregulatory systems, and infections can easily disrupt temperature homeostasis, making temperature instability an important early sign of neonatal sepsis.