Instability of revised Korean Developmental Screening Test classification in first year of life.

Background: Early development is characterized by considerable variability.

Purpose: To investigate the stability of the revised Korean Developmental Screening Test (K-DST) classification of the development of healthy term 4-6 and 10-12 month-old infants.

Methods: This study used data from the Korean Children's Environmental Health study, a nationwide prospective birth cohort study. Sixty-nine healthy term infants (26 boys, 43 girls) underwent two serial tests at 4-6 and 10-12 months of age between August 2017 and December 2019. We divided the entire group into three categories according to the revised K-DST cut-off points.

Results: At 4-5 months, more than 50% of infants were categorized into the ≥-1 standard deviations (SD) group. The lowest prevalence (52.7%) was observed in the gross motor domain. Seven infants (10.1%) scored below -2 SD in at least one domain. The prevalence of scores below -2 SD was 7.3% in the gross and fine motor domains. At 10-12 months, >70% were as categorized into the ≥-1 SD group except in the language domain. Six infants (9.5%) scored below -2 SD in at least one domain. The prevalence of scores below -2SD was 4.8%, 3.2%, 3.2% in the cognition, language, and gross motor domains, respectively. On serial follow-up for 4-12 months, a significant number of infants improved to the peer and high-level group (≥-1 SD), especially in the gross motor domain (33.3%). Among the seven infants who scored below -2 SD at 4-5 months, only two had -2 SD scores at 10-12 months.

Conclusion: For infants presenting with suspected developmental delay on the revised K-DST 4-5 months questionnaire, especially in the gross motor domain, in the absence of any abnormal neurological findings or developmental red flags, close monitoring and repeated assessments should be performed.