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

Background: Early development is characterized by considerable variability.

Purpose: This study aimed to examine the stability of developmental classifications using the revised Korean Developmental Screening Test (K-DST) in healthy term infants aged 4-6 and 10-12 months.

Methods: Data were obtained from the Korean Children's Environmental Health Study, a nationwide prospective birth cohort. Sixty-nine healthy term infants (26 boys, 43 girls) underwent serial K-DST assessments at 4-6 and 10-12 months of age, between August 2017 and December 2019.

Results: At 4-5 months, over 50% of infants were categorized in the ≥-1 standard deviation (SD) group, with the lowest prevalence in the gross motor domain (52.7%). Seven infants (10.1%) scored below -2 SD in at least one domain, most commonly in gross and fine motor domains (7.3%). At 10-12 months, over 70% of infants scored in the ≥-1 SD group, except in the language domain. Six infants (9.5%) scored below -2 SD in at least one domain, (cognition 4.8%, language 3.2%, gross motor 3.2%). Serial follow-up showed significant improvement, with many infants moving to the ≥-1 SD group, particularly in the gross motor domain (33.3%). Of the seven infants scoring below -2 SD at 4-5 months, only two remained in this category at 10-12 months.

Conclusion: Infants scoring below -2 SD on the revised K-DST 4-5 months questionnaire, especially in the gross motor domain, should undergo close monitoring and repeated evaluations in the absence of neurological abnormalities or developmental red flags.