Low birthweight

Almost 25 million low-birthweight (LBW) infants (<2,500 g) are born each year, 95% of them in developing countries [4]. In developing countries, LBW infants are more likely to be born at term than those in developed countries and more likely to be small due to intrauterine growth retardation (IUGR) secondary to maternal undernutrition and infection [5]. The diagnosis of IUGR requires longitudinal measures of intrauterine growth. As these are rarely available in low-income countries, we will restrict this review to infants born at term but small for gestational age (SGA).

A recent review of 80 studies, mostly in developed countries, showed that LEW children generally have poorer levels of development than normal-birthweight (NEW) infants [6]. Fewer studies exist of SGA infants, and they suffer from many design problems. Probably the greatest problem is that researchers have used different definitions for SGA, and there is no generally accepted definition, although the World Health Organization (WHO) recommends using the 10th centile for gestational age [7]. There are also several confounding variables that are frequently not taken into account adequately. SGA babies have a greater incidence of perinatal complications than NEW babies [8,9], which may detrimentally affect their subsequent development [10]; they also come from poorer homes than NEW children and are less likely to be breastfed. A further problem is that samples of SGA children have often been small and had a large percentage of drop-outs [11, 12] that is often biased [ 13]. The babies from the poorest homes and those who have the poorest development are the most likely to drop out. It is surprising that so few studies have been undertaken in developing countries, where SGA infants are more common and the children are exposed to more deprived environments, so that their development may be very different. All aspects of the development of SGA babies were recently reviewed at a meeting of the International Dietary Energy Consultative Group [14-17]. SGA infants were found to suffer from more infections and higher mortality rates in the first year of life than NEW babies [18].