Which factor contributes to a newborn's greater risk of heat loss after birth?

• A. A large body surface area relative to body weight
• B. Thick subcutaneous fat
• C. High percentage of body water
• D. Strong brown fat stores

Answer: (A)

Heat loss in newborns is driven by surface area relative to body weight; a larger SA:BW ratio means more skin is exposed for heat to move into the environment, so heat is lost more quickly.

Heat travels from the baby through radiation, convection, conduction, and evaporation. With a relatively large surface area for a small body, these heat-transfer processes occur more rapidly, increasing the risk of hypothermia after birth.

Other factors influence heat loss, but they work the opposite of increasing risk: newborns have limited insulation because they lack thick subcutaneous fat, they have a high percentage of body water which boosts evaporative loss, and brown fat stores help generate heat—so strong brown fat actually reduces heat loss. The single most impactful factor here is the large surface area relative to body weight.