Neurodevelopmental assessment practices in the longitudinal birth cohort studies at the Children’s Centers were guided by many of the principles outlined above. Most centers conducted neurodevelopmental assessments at various ages after birth (see ). For the first 5 years of funding, most centers conducted assessments at 12 months and 24 months of age.
Neurodevelopmental assessment in the Children’s Centers for the first 5-year funding cycle.
A diverse group of standardized neurodevelopmental assessment tools were employed. There were no attempts to develop common protocols among the centers conducting neuroepidemiologic studies. Differences in tests and timing of assessment reflect variations in the toxicants under study, their hypothesized effects, and practical considerations. Four centers conducted neonatal assessments; three used the NBAS (Brazelton 1984
; Brazelton and Nugent 1995
), and one used the NICU Network Neurobehavioral Scale (Lester et al. 2004
). The Bayley Scales of Infant Development–II (Bayley 1993
), which provides standard scores for mental and psychomotor development, were used by all centers at 12 months of age and by most at 24 months. All centers adjusted the child’s chronologic age for prematurity on the Bayley scales until 24 months.
A variety of other assessment tools were used to measure domains including developmental milestones, language, and behavior. A few centers employed more experimental protocols, including assessment of visual recognition memory, the autonomic nervous system, and measures of learning that parallel some of those used in animal studies. The centers at Illinois and the University of Cincinnati also assess the child’s hearing.
The choice of neurodevelopmental tests was based first on the age of the child, followed by other considerations including tests employed in previous studies, the domains of behavior thought to be affected by the main toxicant(s) under study, the availability of tests in the language of the study population, time required to administer the examination, and the test’s suitability for administration by non-doctoral-level examiners. Some centers, especially those with low-income or bilingual study populations, found it necessary to select assessment tools with a lower end of functioning range, considerably below the ages of the children being assessed.
As discussed above, it can be difficult to determine the language of assessment for children who are raised in the United States in non-English-speaking households. All centers attempted to maximize the child’s performance on all tests. One center assessed bilingual children in English. Another center based the child’s assessment on what language was usually spoken in the home. In both cases, if the examiner noted language difficulties during the exam, the tasks were readministered in the other language.
The availability of assessment tools increases with the child’s age, enhancing the researcher’s ability to focus on specific developmental domains that may be affected by the exposure of interest. Because many of the chemicals examined by these centers have not been widely studied in children (e.g., pesticides, polycyclic aromatic hydrocarbons), the choice of the domains likely to be affected may be based solely on animal studies. Finding the human analog to animal behavior is challenging. However, as previously noted, the Illinois center is addressing this problem by conducting concurrent animal studies with exposures similar to those in their human population.
All centers used some quantitative measures of the parent’s cognitive functioning and quality of caregiving in the home to control for possible confounding. In centers dealing mainly with multicultural samples, tests of adult intellectual attainment with a minimum of verbal content were used.