Thirty-four studies were deemed eligible for inclusion in the review: 23 RCTs (n=2,552), 4 level two studies (n=501) and 7 level three studies (n=202).
Agreement between reviewers for the validity assessment was rated as high using Cohen's kappa (0.86 for judgements of internal validity and 0.95 for external validity).
Internal validity was rated as high in 11 studies, fair in 15 and low in 8. External validity was rated as high in 5 studies, fair in 16 and low in 12.
Interventions applied at the NICU (17 studies).
Two fair- to high-quality RCTs demonstrated a significant positive effect of the intervention on motor outcome. The interventions in these studies focused on stress reduction combined with general sensory stimulation and general infant development using general sensory stimulation, stimulation of motor development, passive handling techniques and enhancement of parent-infant interaction. Five of the 9 studies that were rated as lower methodological quality suggested a positive effect of the intervention. The interventions in these studies included procedures to reduce stress, multimodal sensory stimulation, passive motor intervention strategies, or the facilitation of parent-infant interaction.
Interventions applied between discharge from the NICU and a corrected age of 9 months (8 studies).
Four fair- to high-quality studies evaluated the effects of neurodevelopmental treatment (NDT); however, none found statistically significant effects. Two high-quality studies assessed programmes that stimulated infant motor development; both studies reported statistically significant effects.
Interventions started between the corrected ages of 9 and 18 months (6 studies).
One high-quality study demonstrated a positive effect of specific motor training on motor development of infants with Down syndrome, while another high-quality study found that a general infant stimulation programme facilitated motor development more than NDT. The other high-quality study showed no significant effect. One of the 3 lower quality studies found a beneficial effect of general programmes on stimulating motor development.
Interventions applied between discharge from the NICU and a corrected age of 18 months (3 RCTs).
All 3 studies were rated as moderate to high validity. One study that evaluated NDT for half a year reported a positive effect on motor development.