Physical growth and cognitive abilities in concordant versus discordant birth weight twins at three years old

Discordant birth weight twins have been shown to have high rates of adverse perinatal outcomes, but little is known about their growth and development.

To determine whether smaller and larger birth weight premature twins in concordant and discordant birth weight groups differ on measures of physical growth and intelligence at 3 years.

Prospective cohort study. Eight-four children, 52 concordant and 32 discordant birth weight twin pairs, were measured for height, weight, and head circumference and on intelligence at 3 years. Perinatal and demographic variables, including birth weight, head circumference, small for gestational age, zygosity, in vitro fertilization, gender and social class were recorded.

Smaller and larger birth weight twins did not differ significantly from each other on any growth parameters in either concordant or discordant birth weight groups at 3 years of age. Smaller birth weight twins in the discordant birth weight group performed significantly less well on Verbal, Performance, and Full Scale IQ scores (Verbal IQ for smaller twins was 8.6 points lower, p<0.005; Performance IQ, 11.9 points lower, p<0.03; Full Scale IQ, 12.4 points lower, p<0.004), but there were no significant intra-twin differences between larger and smaller birth weight concordant twins.

Smaller discordant birth weight twins performed significantly less well on intelligence, although they did not differ significantly from their larger twins on growth parameters at 3 years old. We conclude that smaller discordant birth weight twins had less optimal intra-uterine environments than their larger birth weight twin, which affected both their birth weights and brain development.