Final answer:
To prevent heat loss in preterm infants, placing the infant under a radiant warmer is crucial.
Step-by-step explanation:
To prevent heat loss in preterm infants, the crucial intervention is to place the infant under a radiant warmer. This is because preterm infants have a higher ratio of surface area to volume, which makes them more susceptible to heat loss. The radiant warmer helps to provide a controlled environment and maintain the infant's body temperature.