The influence on a ‘normal’ birthweight distribution of a minor population of growth retarded infants: a Monte Carlo simulation

It is common practice to define babies below a certain birthweight as ‘growth-retarded’ or ‘small-for-dates’. This presupposes that there is a specific subpopulation of babies who have not achieved their genetic growth potential. The presence of this subpopulation should result in a deviation from a normal distribution in the population as a whole. We have used a mathematical simulation, together with data from an actual sample of 1463 male Caucasian neonates delivered at 40 weeks, in order to define the characteristics of such a subpopulation which would yield deviations from the normal sufficient to be statistically significant. On the basis of this study, there was no evidence for such a subpopulation of low birthweight babies in the 1463 neonates observed.