Abstract: Twenty-five studies met the inclusion criteria (3615 randomly assigned participants). Only 12 of these studies were randomised controlled trials with appropriate allocation concealment. Variability was evident with regard to focus and intensity of the intervention, participant characteristics and length of follow-up. Meta-analysis led to the conclusion that intervention improved cognitive outcomes at infancy (developmental quotient (DQ): standardised mean difference (SMD) 0.32 standard deviations (SDs), 95% confidence interval (CI) 0.16 to 0.47; P value < 0.001; 16 studies; 2372 participants) and at preschool age (intelligence quotient (IQ); SMD 0.43 SDs, 95% CI 0.32 to 0.54; P value < 0.001; eight studies; 1436 participants). However, this effect was not sustained at school age (IQ: SMD 0.18 SDs, 95% CI -0.08 to 0.43; P value = 0.17; five studies; 1372 participants). Heterogeneity between studies for cognitive outcomes at infancy and at school age was significant. With regards to motor outcomes, meta-analysis of 12 studies showed a significant effect in favour of early developmental interventions at infancy only; however, this effect was small (motor scale DQ: SMD 0.10 SDs, 95% CI 0.01 to 0.19; P value = 0.03; 12 studies; 1895 participants). No effect was noted on the rate of cerebral palsy among survivors (risk ratio (RR) 0.82, 95% CI 0.52 to 1.27; seven studies; 985 participants). Little evidence showed a positive effect on motor outcomes in the long term, but only five included studies reported outcomes at preschool age (n = 3) or at school age (n = 2). Early intervention programmes for preterm infants have a positive influence on cognitive and motor outcomes during infancy, with cognitive benefits persisting into preschool age. A great deal of heterogeneity between studies was due to the variety of early developmental intervention programmes tested and to gestational ages of included preterm infants; thus, comparisons of intervention programmes were limited. Further research is needed to determine which early developmental interventions are most effective in improving cognitive and motor outcomes, and to discern the longer-term effects of these programmes.

Plain-language summary: Twenty-five studies met the inclusion criteria (3615 randomly assigned participants). Only 12 of these studies were randomised controlled trials with appropriate allocation concealment. Variability was noted with regard to focus and intensity of the intervention, participant characteristics and length of follow-up. Evidence suggests that early developmental interventions improve cognitive outcomes up to preschool age. Evidence also indicates that early developmental interventions improve motor outcomes during infancy; however, these effects are small. Little evidence was found of an effect on long-term cognitive or motor outcomes (up to school age). The early developmental intervention programmes described in this review had to begin within the first 12 months of life, had to focus on the parent-infant relationship and/or infant development and, although they could begin while the baby was still in hospital, had to include a component that was delivered post discharge from hospital. The early developmental intervention programmes included in this review vary by content and by frequency and focus of the intervention. This review of 25 trials supports early developmental intervention programmes provided to preterm infants post hospital discharge with the goal of improving cognitive development over the short to medium term (up to preschool age). Variability among these early developmental intervention programmes limits the conclusions that can be drawn about their effectiveness.