Relationship between body size, thermal balance and thermal insulation of term infants under various ambient conditions.

A gradient layer direct calorimetric study was made on the thermal balance of small-for-date, appropriate-for-date and large-for-date term newborn infants during the first 2 days of life. At ambient temperatures of 28 and 32 degrees C, the dry and total heat losses per kilogramme body weight were inversely related to body weight. There was a negative correlation between metabolic rate per kilogramme and body weight, whereas in terms of surface area the correlation became positive. A similar tendency without statistical significance was observed at an ambient temperature of 37 degrees C. In a cool environment (28 degrees C), a significant positive correlation was found between body weight and ambient or total thermal insulations. Tissue and total insulations were inversly related to the metabolic rate. It was concluded that small-for-date newborn infants are handicapped not only by the unfavourable surface-to-mass ratio but also by the limited specific body thermal insulation.