To assess the effect of prenatal and postnatal lead exposure upon early cognitive development of infants using the Bayley Scales of Infant development at the age of 6, 12, 18 and 24 months in a longitudinal study;
Ø To determine the risk of exposure to lead through a detailed questionnaire; and
Ø To identify prevention factors that should be taken into consideration by public health authorities.
Many studies have confirmed that low-level lead exposure in early life can be associated with deficits in neurobehavioral-cognitive performance during childhood and adolescence. Our previous studies confirmed the transfer of lead from the mother to the fetus as well as the effect of low lead exposure on neuropsychological behavior in school children. These results encouraged us to design a longitudinal survey to evaluate the effect of prenatal and/or postnatal lead exposure on early cognitive development among selected group of children from birth to two years of age. During the first stage of this study (between March to July 2004), we measured lead levels in 653 umbilical cord blood samples taken from healthy Saudi mothers delivering at King Khalid Hospital, Al-Kharj. The mean cord lead levels were 2.21 + 1.691 µg/dl in the range of 0.284 to 17.276 µg/dl. Only 1.23% of the newborns had blood lead levels > 10 µg/dl, the Center for Disease Control level of concern. Based on the results of lead levels in the collected cord blood samples, infants were classified into three groups for neuropsychological assessments as follows: the lower and upper 10th percentile of the distribution of cord blood lead level were designated as low (≤1.045 µg/dl) and high (≥ 3.466 µg/dl) lead risk groups. Infants with levels in-between the lower and upper 10th percentile qualified as mid group (>1.045-<3.466 µg/dl). At 6, 12, 18 and 24 months, the Bayley Scales of Infant Development were administered and venous blood lead levels were measured. Demographic, environmental and socioeconomic information was obtained for each infant. Mean blood lead concentrations in the infants increased from 3.36 μg/dl at the age of 6 months to 4.451 μg/dl at the age of 24 months, but the standardized Mental Development Index (MDI) and Psychomotor Development Index (PDI) decreased from 99.26 and 98.13 at the age of 6 months to 93.29 and 82.52 respectively at the age of 24 months. Due to the high rate of attrition, most of the infants in the low group were lost. Therefore, we used the 75th percentile of blood lead levels as a cut-off in the statistical analyses.
Prior to confounding variables adjustments, neither prenatal or postnatal blood lead exposure was related to cognitive development scores. After adjustment for large number of confounding variables, prenatal lead exposure were significantly and inversely associated with the standardized MDI and PDI scores at the age of 6 months old. Borderline significant effect of prenatal lead exposure was also seen on standardized PDI scores at the age of 24 months. On the other hand, no relationship was seen between postnatal blood lead levels and concurrent cognitive development scores. Such observation is not conclusive because of low statistical power due to small sample size. Our results provide an additional evidence for low prenatal lead exposure effects (< 10 µg/dl the CDC level of concern) on cognitive development in Saudi infants living in a rural area. Delayed psychomotor or mental performance in infants is assumed to be an indicator of later neurocognitive development in children, which may persist into adult life. This study suggests that even at low prenatal lead exposure, all possible measures should be taken to study lead sources in our environment and reduce lead exposure. An active environmental policy is required to create more public and professional awareness.

Dr. Mohamed Gamal El-Din
Dr. Michael Nester
Dr. Carolyn Schroeder
Ms Lina Mincari

This study provides an evidence that lowered cognitive development indices of infants at the age of 6 months are associated with low prenatal lead exposure supporting other recent studies (Patel et al 2006; Chiodo et al 2007) that cognitive deficits are seen in blood lead levels much lower than the CDC safe limit (<10 µg/dl). Moreover, existing data indicate that there is no evidence of a threshold for the adverse consequences of lead exposure Lanphear et al (2005). Our studied population may be not be representative of the urban children population in Saudi Arabia because it consisted of rural population of predominantly Saudi infants living in Al-Kharj area with no occupational exposure to lead. Hence, the results cannot be generalizable to other children. However, it might reflect typical exposure in rural settings. On the other hand, the groups of infants under comparison did not significantly differ with respect to important confounders such as socio-economic and demographic factors, which might affect child development. The results require confirmation but are of potential concern because delayed psychomotor or mental performance in infants is assumed to be an indicator of later neurocognitive development in children, which may persist into adult life as shown in other studies. Furthermore, we hope that the results of this study will draw the attention of physicians to potential toxic effect of lead or other neurotoxic pollutants such as mercury when evaluating children with neurological symptoms of unclear causes. Awareness of lead exposure and its health hazards is uncommon, not only in the population at large, but also among pediatricians and public health workers.
However, the results require confirmation in additional longitudinal study with a larger sample size through school age in order to determine whether developmental delays are associated with educational or social problems. Through the early identification of infants at risk, we hope to be able to reduce adverse lead effect.

King Faisal Specialist Hospital & Research Center

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"Longitudinal Study of Prenatal and Postnatal Lead Exposure and Early Cognitive Development in Al-Kharj, Saudi Arabia: A Preliminary Results of Cord Blood Lead Levels" in  Journal of Tropical Pediatrics Advance Access published March 18, 2008

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