A comparison of sleep and settle behaviors across twins and singletons at 5 months of age

Twin studies have made important contributions to knowledge regarding the role of genetic and environmental influences on child development. It is important to test the assumption that findings can be generalized from twins to singletons in infancy. The first months of life are defined by significant developmental changes and the emergence of important sleep behaviors. As such, we compared 451 twins and 77 singletons on a range of sleep, settle, and crying behaviors at five months of age. No statistically significant differences between twins and singletons were found regarding duration of crying or time until settled during different times of the day. However, singletons were reported to wake up more frequently during nighttime than twins (F(1, 509) = 35.10, p <.001), 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 behaviors at five months of age.