Distribution of nutrients between fetal brain body during rat development

During prenatal development, the distribution of nutrients between brain and body is influenced by many factors. Fetal and neonatal ratios may serve as indices of the final outcome; brain weight/body weight (Rw), brain DNA/body DNA (RDNA) and brain protein/body protein (Rprot; similar to Rw). These ratios decrease with fetal age but this dependence on age disappears towards term. Within one age, these ratios show considerable variability (up to 14%), from litter to litter, and within litters. The variability is not due to variation in water contents ( less than 1%). An extensive study of 2,089 normal newborns revealed that 7.5% had Rw values significantly higher than the mean for the population. Of these, 35% had normal body weights but significantly higher brain weights. Thus, they do not represent previously studied cases of general (brain and body) overdevelopment; rather, they represent cases of favorable brain versus body growth, i.e. distribution of nutrients between brain and body that is more favorable for the brain. Such a favorable distribution may be caused by maternal factors if it affects entire litters (3% of all affected) or by fetal factors, if it affects only individuals within a litter (49%).