Abstract
BACKGROUND: Global Developmental Delay (GDD) affects cognitive, language, motor, and adaptive functions in children under five years and is often a precursor to long-term neurodevelopmental disorders including intellectual disability and autism spectrum disorder. Early intervention can improve developmental outcomes, yet evidence regarding its effectiveness, especially in low-resource and diverse clinical settings, remains fragmented. To synthesize available evidence on the effectiveness of early intervention programs for children aged 0-6 years with GDD, and to identify intervention types, outcomes, and gaps in current research. MATERIALS AND METHODS: A systematic review following PRISMA 2020 guidelines was conducted. PubMed, Web of Science, Scopus, and ClinicalTrials.gov were searched up to October 14, 2025, using predefined search terms. Eligible studies included children aged 0-6 years diagnosed with GDD or nonspecific developmental delay and involved an early intervention program assessing developmental outcomes. Data extraction and quality appraisal were performed using Joanna Briggs Institute (JBI) tools. Narrative synthesis was used due to heterogeneity across studies. RESULTS: Six studies involving a total of 689 participants were included. Interventions varied widely, including multidisciplinary rehabilitation, parent-mediated programs, community-based approaches, and combined medical-therapeutic methods. All studies reported improvements in at least one developmental domain (motor, language, cognitive, or social), with greater gains observed when interventions were initiated early (6 months) and sustained over longer durations. Parent-mediated and community-based models were feasible and effective in low-resource settings. However, no randomized controlled trials were identified, and most studies showed moderate to high risk of bias. Certainty of evidence was rated low to very low using GRADE. CONCLUSION: Early intervention programs demonstrate consistent benefits for children with GDD across settings, particularly when initiated early and involving caregivers. However, the current evidence base is limited by methodological weaknesses and lack of standardized outcome measures. High-quality randomized trials and long-term follow-up studies are urgently needed to inform best practices and policy implementation.