Which process causes the greatest source of heat loss immediately after birth?

• A. Convection
• B. Evaporation
• C. Radiation
• D. Conduction

Answer: (B)

Evaporation is the fastest way a newborn loses heat right after birth. The baby is wet with amniotic fluid, and as this moisture changes to vapor it absorbs a lot of heat from the skin (latent heat of vaporization), causing rapid cooling. The newborn’s surface area-to-mass ratio is large and its thermoregulation is immature, so this evaporative heat loss is substantial in the immediate postnatal period. Once the infant is dried and kept warm—such as with skin-to-skin care, radiant warming, and dry coverings—evaporative losses decrease. After drying, heat loss shifts more to convection (air moving around the infant), radiation (toward cooler surrounding objects), and conduction (contact with cold surfaces), but evaporation remains the dominant early mechanism.