Twin-Singleton Comparisons Across Multiple Domains of Life

Abstract

In this chapter, we address the question whether individuals born from a multiple pregnancy differ from singletons. The answer to this question is important for health-care professionals and researchers, as well as multiples themselves and their family members. First, we review findings from the literature with respect to twin – non-twin differences in early life and conclude that a multiple pregnancy increases the risk of congenital problems and mortality for the unborn and newborn children. Next, we provide an overview of the outcomes of comparing adult twins to their singleton siblings across a wide range of traits assessed in the Netherlands Twin Register (NTR). In a within-family design, comparing twins to siblings from the same family, we correct for familial confounding. Overall, hardly any evidence was found for the presence of twin-sibling differences for the five domains explored, which included body composition and physical development, personality and psychopathology, behavioral and sociodemographic traits, physiological parameters and physical disease, and cognitive function. With the exception of minor differences in body composition, twins do not seem to differ from singletons, when taking family factors into account. In conclusion, while being a twin can be seen as special, adult twins are similar to ordinary siblings across most domains of life.