Physical growth and intelligence development of discordant dizygotic twins from birth to preschool age: a prospective cohort study

Background The majority of studies are limited to adverse perinatal outcomes and poor cognitive abilities in the short term in discordant monochorionic twins. Methods To determine whether small and large discordant dizygotic twins differ in physical growth and intelligence development and weight and height from birth up to 6 years of age were measured in 34 dizygotic twin pairs with >= 20% birth weight discordance. Mental developmental index (MDI) and psychomotor developmental index (PDI) were calculated at 1 year, while the Wechsler Intelligence Scale for Children-IV (WISC-IV) full-scale intelligence quotient (IQ) was assessed at the age of 6. Results The difference in height and weight in each stage differed significantly from birth to 72-months-old (P < 0.05), although there was disappointing catch-up growth in smaller twins. PDI but not MDI at 1 year of age was significantly different between the two groups (P < 0.05), and smaller twins experienced higher psychomotor retardation rates (P < 0.05). Also, the influence of height and weight on PDI was statistically significant (P < 0.05). No significant difference was detected in the WISC-IV full-scale IQ at the age of 6; however, the full-scale IQ may be affected by the history of suffocation and the S/D value (P = 0.011, P = 0.022). Conclusions Intrauterine fetal growth and development lead to birth weight differences in twins and sustain an impact on the children's physical growth in height and weight from birth to preschool age, causing psychomotor developmental differences at 1 year of age. However, the differences in psychomotor development decrease gradually by the age of 6.