A Comparison of Sleep and Settle Behaviours Across Twins and Singletons at 5 Months of Age

ABSTRACT Twin studies are important for research on genetic and environmental influences on child development, but it is imperative to test whether findings can be generalised from twins to singletons. Since the first months of life are defined by the emergence of important sleep behaviours, we compared 451 (54.8% females) twins and 77 singletons (48.1% females) on a range of sleep, settle and crying behaviours at 5 months of age. No significant differences were found regarding duration of crying or time until settled. However, singletons were reported to wake up more frequently during nighttime than twins ( F (1, 509) = 35.10, p < 0.001, η p 2 = 0.065), suggesting that, when reported in twin studies, this measure might be slightly underestimated at a mean level in relation to singletons. In conclusion, despite the unique challenges and additional caregiver load of infant twins, there seem to be few differences between twins and singletons regarding parent‐reported settle and crying behaviours in early infancy.