Neurodevelopmental Outcomes of Twins Compared With Singleton Children: A Systematic Review

Area of Science:

• Developmental Psychology
• Pediatrics
• Neuroscience

Background:

• Over 200 million children under five fail to reach their full cognitive potential.
• Children born as twins are identified as a population at higher risk for neurodevelopmental disparities.
• Existing research presents conflicting findings regarding twin and singleton neurodevelopmental outcomes.

Purpose of the Study:

• To review and synthesize existing studies comparing neurodevelopmental outcomes of twins and singletons.
• To identify factors influencing observed differences or lack thereof in cognitive development.
• To highlight limitations in current research and suggest directions for future studies.

Main Methods:

• A systematic literature search was conducted on the Medline database using keywords: twins, singletons, neurodevelopment, and cognitive development.
• Bibliographies of relevant publications were inspected for additional studies published between 2011 and 2017.
• Eight studies met the inclusion criteria, encompassing prospective follow-up, cross-sectional, and randomized controlled trial designs.

Main Results:

• Five studies from developed countries found no significant neurodevelopmental differences between twins and singletons.
• Two of three studies from developing countries indicated singletons had significantly higher academic ratings than twins.
• Early-life assessments (1-5 years) showed no significant twin-singleton differences, whereas later assessments yielded mixed results.

Conclusions:

• Neurodevelopmental outcomes for twins and singletons may differ based on geographical location (developed vs. developing countries).
• The timing of neurodevelopmental assessment appears to influence observed differences between twins and singletons.
• Current studies may be underpowered and lack optimal design, necessitating larger, well-designed research to resolve conflicting findings.