Determinants and components of size at birth
Many publications contain standards of birthweight of widely different populations, whilst others investigate the effects of specific factors on birthweight. A large number of these publications were reviewed, with particular reference to those which have attempted to incorporate some of the determinants of birthweight into their published standards.The first study compares the use of the analysis of variance andmultiple regression to establish standards of birthweight which take account of the effects of maternal height, weight, age, parity, gestation and sex of the baby, based on the data of 12,918 babies. Multiple regression analysis appears to be the more valid model on which to base standards of birthweight, as it allows for correlation between variables. When compared to standards of birthweight basedon gestation alone, the increase in precision obtained by incorporating five further variables into the model is statistically significant but small (standard error 420 grams : 447 grams).It is argued that there is therefore a need to explore variation in size of the neonate in a more discreet manner than simply referring to birthweight. The second study explores the data of 301 neonates, each with 27 measurements, using a number of factor analytical models. Factor analysis has the advantage over intuitive or theoretical classifications that it defines the dimensions of size of the neonate on empirical grounds, based on relationships within the data. The results suggest seven possible dimensions which are best represented by the following measurements: chest circumference, nuchal-rump length, head circumference, lower leg length, upper arm length, thigh skinfold thickness and abdominal skinfold thickness. Application of these results to clinical data suggests that they may offer the basis of a classification of neonatal size.