Bayley Psychomotor Development

A subset of possible predictor variables was then identified and this included home environment assessment score at year 1 (HOMEl) and year 2 (HOME2), obstetric complication score, birth weight, birth order, socioeconomic class of the father in year 1 (SCI) and in year 2 (SC2). The dependent variables considered were Bayley mean score at year 1 and year 2, Bayley Mental Development Index (MDI) at year 1 and year 2 and the Bayley Psychomotor Development Index (PDI) at year 1 and year 2. The overall mean scores at year 1 and year 2 were significantly correlated (r = 0.39). The mean values for these dependent variables are set out in Table 3. 

The follow-up evaluations at both 6 and 12 months included the administration of the Bayley Scales of Infant Development (Gladen et al. 1988). This exam yields a mental development index (MDl) score and a psychomotor development index (PDI) score, both of which are scaled like a standard IQ test. There were 858 infants (92%) from the original cohort who participated in the study past the neonatal period. 

To assess the mental and psychomotor development of infants exposed to PCBs both pre- and postnatally, the Dutch standardized version of the Bayley Scales of Infant Development were administered at 3, 7, and 18 months of age. Both the MDI and the PDI were included in the assessments. The tests were performed at the infant s home in the presence of the parent(s) (Koopman-Esseboom et al. 1996). The evaluations of the infants using the Bayley Scales of Infant Development were undertaken only for the 207 children from Rotterdam. Rotterdam is an urban area thought to have higher exposures to PCBs than Groningen, a semi-urban area in northern Holland. 

As mentioned above, age norms for the Spanish population have been developed for Cattell s test as well as for Bayley s (0-2%-year-olds) and McCarthy s (2%-6-year-olds) tests. Test performance on the two latter test series is represented by a Mental Development Score and a Psychomotor Development Score. 

Measures chosen were comparable with those used in the other longitudinal studies being conducted The Bayley Scales of Infant Development (1969) were used to measure mental and psychomotor development at 6 months, 12 months and 24 months the Bayley Infant Behaviour Record and the Toddler Temperament Questionnaire (Fullard et al, 1978) to monitor behavioural problems. At 3 years the McCarthy Scales of Children s Abilities (1972) replaced the Bayley Scales, and this test was employed also at 4 years and, currently, at 5 years. At 5 years a special computer vigilance task is being employed to assess attention span and attain reaction time measures. (This task was written by Jacobson and Jacobson at Wayne State University, Detroit, USA.)... 

In an interim study of 185 innercity infants in Cincinnati, Ohio, we previously reported (Dietrich et al, 1986) an Indirect adverse effect of prenatal lead exposure on the 6-month Bayley MDI and Psychomotor Development Index (PDI). The effect was mediated by lead-related deficits in foetal growth (birth weight) and maturation (gestational age by physical examination). These relationships are illustrated by the structural equation model shown in Figure 1. 

Nearly all tests used for assessing the children s mental level had, at an earlier stage, been adapted to the Spanish population that was the case with, for example, the Bayley Scales of Infant Development, the McCarthy Scales of Children s Abilities, and Cattell s Culture Fair Intelligence Test. Some of the psychomotor tests that were not adapted to Spain were included in the survey anyway because of their expected relevance. 

At age 24 months, the developmental status of each child was formally measured using the mental (MDI) and psychomotor (PDI) subscales of the Bayley Scales of Infant Development (Bayley, 1969). These scales were administered to all children by one clinical psychologist who has remained blind to blood lead results throughout the study. Testing was undertaken on a different day from that on which other interviewing and blood collection took place. 

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