A systematic review and meta-analysis of the associations between motor milestone timing and motor development in neurodevelopmental conditions.

Early motor skills may be important early markers of neurodevelopmental conditions or predictors of their later onset. To explore this, we conducted a systematic review and meta-analysis of infant motor skill assessments in those who go on to gain a clinical diagnosis of autism, attention deficit hyperactivity disorder (ADHD), schizophrenia, language conditions, tic disorders, or developmental coordination disorder (DCD). In total, 63 articles met inclusion criteria. Three three-level meta-analyses were run. Meta-analysis of milestone achievement in N= 21205 individuals revealed gross motor milestones were significantly delayed compared to controls (g= 0.53, p< 0.001). Subgroup analyses revealed autism (g= 0.63) and DCD (g= 0.53) had the highest magnitude delays. Specific delays were revealed for holding the head up (g= 0.21), sitting (g= 0.28), standing (g= 0.35), crawling (g= 0.19), and walking (g= 0.71). Meta-analyses of standardised motor skill measurements in N= 1976 individuals revealed reduced performance compared to controls in autism and language conditions (g= -0.54, p< 0.001). Together, these findings demonstrate delayed milestone attainment and motor impairments in early childhood in neurodevelopmental conditions.