Association between birth weight and neuromotor performance: a twin study

Studies have shown important associations between low birth weight (BW), a variety of morbidities, and reduced motor performance. Using a twin sample, this study aimed to verify (a) the magnitude of the association between BW and neuromotor performance (NMP); (b) if the NMP of twins is within the normal range; and (c) if monozygotic (MZ) and dizygotic (DZ) twins' intra-pair similarities in NMP are of equal magnitude. We sampled 191 twins (78 MZ; 113 DZ distinguished through their DNA), aged 8.9 ± 3.1 years with an average BW of 2246.3 ± 485.4 g; gestational characteristics and sports practices were also assessed. The Zurich Neuromotor test battery, comprising five main tasks, was used; Twins NMP assessments were highly reliable (intra-rater reliability: 0.76-0.99). BW accounted for up to 11% of the total variance of NMP across the zygosity groups. Between 32.7% and 76.9% of children were below the 10th percentile for tasks requiring timing of performance (purely motor task, adaptive fine motor task, dynamic, and static balance), while less than 6.4% of children were below the 10th percentile for associated movements. MZ twins NMP intraclass correlations showed greater similarity than DZ twins in three of the five tasks, suggesting the importance of genetic factors in NMP.