The growth of twins between the ages of 2 and 9 years

Background: Twin growth studies are mostly based on pooled data without consideration of zygosity, parental heights or birth weight. Aim: The study investigated the effects of gender, zygosity, parental height and birth weight on subsequent twin growth. Methods: Height and weight measurements of 1533 twins (n=1077 for occipito-frontal head circumference (OFC)), age range 2-9 years, were converted to standard deviation scores derived from singleton standards. Their growth was evaluated in relation to gender, zygosity, parental heights and birth weight. Results: Mean stature of twins fell only slightly below the reference values of singletons, but they were underweight to a greater extent (boys more than girls). Twins' OFC were low (girls more so than boys). Monozygotic (MZ) twin boys were lighter and shorter than dizygotic twins and MZ twin girls. Deficient growth was most evident in those babies light at birth. Parental heights only partly accounted for the difference in height of twins. Conclusions: Birth weight and parental height are important in relation to subsequent growth. Boy twins are at a disadvantage compared with girls in terms of their growth in height and weight, particularly in the low birth weight and MZ groups.