Categories of intrauterine growth retardation

Abstract

Originally all low birthweight infants were considered to be premature. When prematurity was redefined in terms of gestational age (SGA) and not preterm. With the large scale collection of obstetric data the distributions of birthweight at different gestational ages were described and from these, infants who were SGA could be defined. SGA became synonymous with terms such as growth retardation, but it soon became appearent that the two were not necessarily interchangeable. Scott and Usher found that it was the degree of soft tissue wasting rather than birthweight that related to poor perinatal outcome. Miller and Hassanein stated that: “birthweight by itself is not a valid measure of fetal growth impairment”. They used Rorher’s Ponderal Index (weight (g) × 100/length (cm)) to diagnose the malnourished or excessively wasted infants with reduced soft tissue mass. Most studies of intrauterine growth retardation (IUGR) still use low birthweight for gestational age centile as their only definition of IUGR or only study infants who have a low birthweight. Altman and Hytten expressed disquiet about this definition and stated: “There is now an urgent need to establish true measures of fetal growth from which deviations indicating genuine growth retardation can be derived” and that “it is particularly important that some reliable measures of outcome should be established”. In large series of term deliveries published recently, two groups of IUGR infants with different growth patterens have been identified. These studies confirm that birthweight alone is inadequate to define the different types of IUGR. They established that low Ponderal Index (PI) is a measure of IUGR associated with an increased incidence of perinatal problems and that it is time to re-evaluate IUGR in terms of the different types of aberrant fetal growth.