Attainment of smiling and walking in infancy associates with developmental delays at school entry in moderately-late preterm children: a community-based cohort study

BACKGROUND: Moderately-late preterm (MLP) children (gestational age [GA] 32–36 weeks) are followed-up within community services, which often use developmental milestones as indicators of delay. We aimed to examine associations of parental report of smiling-age and walking-age with developmental delay upon school entry for MLP and full-term children. METHODS: This study regards a community-based cohort study, including 1241 children. Parent-reported smiling-age (n = 514) and walking-age (n = 1210) were recorded in preventive child healthcare. To determine developmental delay at school entry (at age 4) we used the Ages and Stages Questionnaire (ASQ) total and domain scores. We assessed the association of smiling-age and walking-age with dichotomized ASQ-scores, using logistic regression analyses. RESULTS: For MLP children, each week later corrected smiling-age was associated with a relative increased likelihood of delays of 31, 43, 36 and 35% in the personal-social, problem-solving, gross motor and general developmental functioning, respectively. Each month later corrected walking-age was associated with a relative increased likelihood of delays of 10, 15 and 13% in the personal-social, gross motor and general developmental functioning, respectively. All corrected smiling-ages and walking-ages were within normal full-term ranges. For full-term children, we only found that later walking-age was associated with delays in the personal-social and gross motor domains. CONCLUSIONS: Smiling-age and walking-age are associated with developmental delay in several domains for MLP and full-term children. Professionals could use these milestones to identify children that may benefit from closer monitoring of their development. TRIAL REGISTRATION: Clinical Trial Registry name and registration number: controlled-trials.com, ISRCTN80622320.