Definitions used

LBW:

There has been inconsistency in the past regarding the definition of LBW, but a weight of < 2500 g at birth is now widely accepted. Several of the studies referred to in later sections of the text, however, have defined LBW as £ 2500 g and used birthweight intervals of 1001-1500 g etc. These 1g differences will be ignored and the intervals will be presented as 1000-1499 g etc.

IUGR:

There is no agreement as to the definition of IUGR but it may be defined as a birth weight > 2SD below the median for gestational age. Some investigators use the 3rd or 5th centiles, but many use the 10th centile as the cut-off point which will result in some small but normal newborns being wrongly designated as growth-retarded. This inconsistency in the cut-off hampers comparative analysis. A further hindrance is that at least a dozen reference populations are used, and some differ substantially. For example, the 10th centile birth weights for boys at 40 weeks gestation are 2630 g and 3030 g respectively for the reference populations of Lubchenco et al (Denver) and Arbuckle et al (Canada) (World Health Organization, 1995). The reasons for these differences are well established (World Health Organization, 1995; Miller, 1981; Rosso, 1989). For all the reference populations, the 10th centile exceeds 2500 g. In this review, the descriptor will be indicated where possible to facilitate interpretation.