Relationship between metabolic rate and body size in fetal life

To define the O2 consumption rate (VO2) versus body mass relation during fetal growth, we compared fetal sheep VO2 at mid and late gestation. VO2 per kg wet weight was 37% higher at mid gestation. However, VO2 per kg dry weight was 2.5 times higher, and associated with a high viscera/body weight ratio. Fetal VO2 tends to grow proportionally to body mass because marked decreases in the relative growth of visceral organs and in the VO2/dry weight ratio are accompanied by a decrease in body water.