**Core Concept**
Newborn infants are prone to hypothermia due to their large surface area relative to body mass, and their inability to regulate their body temperature effectively. This is because they lack the mature hypothalamic-pituitary-adrenal axis, which is essential for thermoregulation.

**Why the Correct Answer is Right**
Newborn infants prevent hypothermia by using various mechanisms, including the "heat shield" effect of the vernix caseosa, which is a thick, waxy coating on their skin that helps to insulate them. Additionally, the newborn's skin has a thick layer of subcutaneous fat, which also helps to retain heat. Furthermore, the newborn's circulatory system is in a state of vasodilation, which helps to increase blood flow to the skin and promote heat loss.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not provide a specific mechanism by which newborn infants prevent hypothermia.
**Option B:** This option is incorrect because it is not a recognized mechanism for preventing hypothermia in newborn infants.
**Option C:** This option is incorrect because it is not a specific enough answer, and does not provide a clear explanation of how newborn infants prevent hypothermia.

**Clinical Pearl / High-Yield Fact**
It is essential to keep newborn infants warm, especially in the first few hours after birth, to prevent hypothermia and its associated complications. This can be achieved by using a warm blanket or a heating pad, and by keeping the delivery room at a warm temperature.

**Correct Answer: D. The "heat shield" effect of vernix caseosa and the thick layer of subcutaneous fat.**