Birthweight and psychological distress in adult twins: a longitudinal study

Aim: To assess the relation between birthweight and psychological distress as measured by the Malaise Inventory in adult twins. Methods: Data were drawn from the 1958 British birth cohort study, which included twins followed from birth to age 42 y. We examined the relation between birthweight and psychological distress at ages 23, 33 and 42 y measured by the psychological scale of the Malaise Inventory. Analyses were performed both between subjects (n = 282) and within twin pairs (n = 112). The generalized estimating equations approach was used to handle the repeated measurements. Results: Between the 282 twins, the difference in psychological distress score was -0.45 (95% confidence interval -0.74 to -0.15) per Z-score increase in birthweight-for-gestational age. Within twin pairs, the heavier co-twins tended to have a psychological distress score lower than that of their lighter co-twins, the mean difference being -0.35 (-0.78 to 0.09). Conclusion: Results from the between-subject analysis agreed with previous findings from adult singletons that psychological health is related to birthweight. The within-pair analysis suggested a similar relation but did not attain statistical significance.