In population-based studies, the prevalence of neurodevelopmental disabilities is consistently higher in twins than in singletons. This has been linked to the fact that twins are often born preterm and with lower birth weights, both of which are known risk factors for later developmental issues. Although more recent studies indicate small or no differences in developmental outcomes between twins and singletons when controlling for gestational age and birth weight, conflicting results persist. Additionally, it is still uncertain whether certain twin characteristics (such as chorionicity, birth order, and weight discordance) pose additional developmental risks.


The goal of this study is to compare the neurodevelopmental outcomes of twins and singletons in a cohort of preterm infants, born before 34 weeks gestational age, at the age of 2 years, as well as to assess the developmental outcomes of twins based on their order of birth.


The study included 113 infants (34 twins and 79 singletons) born from January 2015 to October 2022, who were treated at the University Hospital Centre Zagreb and enrolled in the follow-up program at the same institution. Exclusion criteria included major brain lesions and malformations, genetic syndromes, and single-twin survivors. Developmental assessments were conducted at corrected age of 24 months using the Bayley Scales of Infant Development-III.


At the 24-month follow-up, there was no significant difference in cognitive, language, or motor outcomes between twins and singletons, and order of birth did not affect developmental outcomes. Our results align with other studies showing no differences in developmental outcomes between twins and singletons. These findings suggest that being a twin does not inherently increase developmental risk beyond the factors associated with preterm birth itself and may contribute to a better understanding of the factors affecting twin development.