Aims--To investigate the relation between haemoglobin in children followed longitudinally from 8 to 18 months, and developmental outcome at 18 months.
Methods--The Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC) is a longitudinal survey of a geographically defined population of children born in 1991-92. In a randomly selected subsample, blood samples were assayed for Hb at 8, 12, and 18 months; a developmental assessment was carried out at 18 months on 1141 children using the Griffiths Scales of Mental Development.
Results--There was a strong quadratic association between Hb at 8 months and performance on the locomotor subscale at 18 months. Average scores increased with increasing Hb up to 95 g/1; there was little additional developmental benefit in Hb levels beyond 95 g/l. Infants with Hb [less than]95 g/1 at 8 months of age scored on average 6 points lower on the locomotor subscale than infants with Hb [greater than or equal to] 95 g/1; infants with Hb [less than]90 g/1 at 8 months scored 12 points lower on the locomotor subscale than children with Hb [greater than or equal to] 90 g/1.
Conclusions--Low Hb concentrations ([less than or equal to] 95 g/1) in 8 month old children are associated with impaired motor development at 18 months. This cut off point corresponds to the 5th centile of Hb at 8 months. The results indicate that if there is an adverse effect of low Hb on developmental outcome, screening may be more effective at 8 months or earlier, rather than after this age. We propose to examine the importance of infant anaemia in relation to more accurate and detailed long term outcomes as the children get older.
(Arch Dis Child 2001;84:480-485)
Keywords: anaemia; development; haemoglobin; screening
Iron deficiency anaemia is the most common nutritional deficiency in the developed world and is a particular problem in preschool children living in inner city areas.  Estimates of the prevalence of anaemia in infants varies between 12% and 30% according to the population studied  and the cut off used to define anaemia. 
The evidence associating iron deficiency anaemia with poor developmental outcome in children is mounting. A number of studies carried out both in developing countries, [4-6] and in Britain  have shown that varying degrees of anaemia in young children are associated with poor cognitive and non-cognitive outcomes. Although under some circumstances iron supplementation has been shown to partially reverse the damage, [8-11] a general consensus has yet to be reached on causation, as the relation between anaemia and development is complicated by multiple confounding variables. A number of animal studies have shown physical and functional effects of poor nutrition on the developing brain, particularly affecting arousal and reactivity.  The brain of the iron deficient rat shows impaired myelination, and altered neurotransmitter function, particularly if the iron deficiency exists during the brain growth spurt between 10 and 28 days of life. Results from a recent study suggest that a chronic marginal iron deficiency during the pre- and post-natal development of mice can result in functional changes in motor development, even in the absence of iron deficiency anaemia. 
Although studies of early diet in humans have shown negative effects of poor nutrition on developmental outcome later in childhood,  there is little evidence to implicate iron deficiency in the absence of anaemia with subsequent developmental impairments.  Questions as to whether a critical period of vulnerability to iron deficiency exists during the human brain growth spurt, and what degree of anaemia caused by iron deficiency is needed to impair development, have yet to be satisfactorily answered.
This study examines the relation between haemoglobin concentrations at 8, 12, and 18 months of age and subsequent developmental outcome at 18 months. Specifically, we explore whether a critical period of vulnerability to anaemia exists in the first 18 months and if so, what degree of anaemia is required to observe impaired development.
All births in the former Avon Health Authority area with an expected date of delivery between 1 April 1991 and 31 December 1992 were eligible for the Avon Longitudinal Study of Pregnancy and Childhood (ALSPAC). Over 80% of the known births from the geographically defined catchment area were included, resulting in a total cohort of 14 138 surviving live births. From the population cohort, a 10% sample of randomly selected parents whose babies were born within the last six months of the survey were invited to bring their children to a research clinic (Children in Focus) at 4, 8, and 12 months of age and six monthly intervals thereafter, where a number of clinical, physiological, and developmental assessments were carried out. For this study, data were obtained from infants attending the 8, 12, and 18 months clinics. Of those invited, 1312 (83%), 1241 (89%), and 1181 (86%) children at tended the clinics at 8, 12, and 18 months old respectively. The mean ages of children attending the 8, 12, and 18 month clinics were. 35, 54, and 80 weeks old, respectively.
A heel prick sample of capillary blood was taken from the children and collected into an EDTA …