Aim: To determine the size of the growth deficit in Dutch monozygotic and dizygotic twins aged 0-2.5 years as compared to singletons and to construct reference growth charts for twins.
Methods: Growth of twins was studied using longitudinal data on over 4000 twins aged 0-2.5 years of the Netherlands Twin Register. The LMS method was used to obtain growth references for length/height, weight, and body mass index (BMI) for twins.
Results: During the first 2.5 years of age, differences in length/height and weight between twins and singletons decrease but do not disappear. BMI of twins deviates less than that of singletons. Approximately half of the growth retardation from birth until 1.5 years of age was attributable to gestational age. Between 1.5 years and 2.5 years of age, this difference was reduced to one-third. Thus, a substantial part of the growth difference could not be explained by gestational age.
Conclusions: During the first 2.5 years of life, there is a difference in growth between twins and singletons. Twins catch up in their body size, i.e. they grow faster after birth, but do not yet achieve the same height and weight till they reach 2.5 years of age. We recommend the use of the growth references for twins.