CDBC/BCAAN Educational bite: Originally emailed July 18, 2024

Global developmental delay (GDD) is a provisional diagnosis in the DSM that should be used for infants and children 4 years of age and younger where children are not meeting expected developmental milestones in several areas of intellectual functioning. At this age, it is difficult for many children to participate in formal assessment. Test scores are less stable compared to scores for older children (please see the bonus educational bite below, and the previous Bite). Even if a diagnosis of intellectual developmental disorder can be established under age 5, it can be challenging to establish a level of disability. GDD can be diagnosed by a physician or psychologist. When given by an evaluating psychologist, a diagnosis of GDD can be used to apply for services through Children and Youth with Support Needs (CYSN), although a re-evaluation will be necessary to ensure continuity of services when the child is older. Of note, GDD is equivalent to the International Classification of Diseases’ (ICD) diagnosis “unspecified IDD.”

While there is typically good reason to wait to confirm a diagnosis of intellectual developmental disorder (IDD), a diagnosis can be made under age 5, typically when there is robust evidence for disability, and there is also a medical/genetic condition known to be highly co-morbid with IDD.

When the evaluating psychologist identifies an intellectual developmental disorder in a child 5 or older, but cannot reliably assess the degree of the impairment (mild, moderate, severe, profound), unspecified intellectual developmental disorder is the appropriate DSM diagnosis. Of note, with unspecified IDD, the diagnosis of IDD is made with full confidence, it is the degree of the disorder which is unclear. While the DSM notes that this category requires re-assessment “after a period of time,” if the diagnosis is made firmly for good reason, it should be accepted by CYSN and Community Living BC (CLBC). The psychologist’s report should clearly state the reason for the “unspecified” diagnosis. The unspecified category is rarely used, as the degree of the disorder should be diagnosed based on adaptive functioning. Unspecified IDD and GDD are mutually exclusive categories (GDD for under 5, unspecified IDD for 5 and older), and the DSM’s “unspecified IDD” aligns with the ICD’s “other IDD.”

Bonus Research Bite: Early developmental assessment (using the Bayley) and the prediction of later IQ scores

• When comparing the Bayley-III score at age 2 to the WPPSI score at age 4, only 81% of preterm children retained the same developmental classification (Bode et al., 2014).
• In preterm children, “Bayley-III cognitive and language scores correlate with later IQ, but may fail to predict delay or misclassify children who are not delayed at school age” (Lowe et al., 2023).
• The Bayley-III at age 3 strongly correlated with WISC-IV FSIQ at age 6 in very low birthweight children. This study suggested that those with Bayley scores 85-95 did not all end up in the average range on the WISC (some were lower scoring on the WISC; Nishijima et al., 2022).
• In typically developing children, the Bayley-III Cognitive scores were correlated with WISC-IV Full-Scale IQ (r = .41), and accounted for 24% of the total Full-Scale IQ variation. This study concluded that the Bayley was an insufficient predictor of later IQ (Månsson, et al., 2019).

References

Bode, M. M., DʼEugenio, D. B., Mettelman, B. B., & Gross, S. J. (2014). Predictive validity of the Bayley, Third Edition at 2 years for intelligence quotient at 4 years in preterm infants. Journal of developmental and behavioral pediatrics : JDBP, 35(9), 570–575. https://doi.org/10.1097/DBP.0000000000000110

Lowe, J., Bann, C. M., Dempsey, A. G., Fuller, J., Taylor, H. G., Gustafson, K. E., Watson, V. E., Vohr, B. R., Das, A., Shankaran, S., Yolton, K., Ball, M. B., Hintz, S. R., & Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network (2023). Do Bayley-III Composite Scores at 18-22 Months Corrected Age Predict Full-Scale IQ at 6-7 Years in Children Born Extremely Preterm?. The Journal of pediatrics, 263, 113700. https://doi.org/10.1016/j.jpeds.2023.113700

Månsson, J., Stjernqvist, K., Serenius, F., Ådén, U., & Källén, K. (2019). Agreement Between Bayley-III Measurements and WISC-IV Measurements in Typically Developing Children. Journal of Psychoeducational Assessment, 37(5), 603-616. https://doi.org/10.1177/0734282918781431

Nishijima, M., Yoshida, T., Matsumura, K., Inomata, S., Nagaoka, M., Tamura, K., Kawasaki, Y., & Makimoto, M. (2022). Correlation between the Bayley-III at 3 years and the Wechsler Intelligence Scale for Children, Fourth Edition, at 6 years. Pediatrics international : official journal of the Japan Pediatric Society, 64(1), e14872. https://doi.org/10.1111/ped.14872