Growth trajectories in monochorionic and dichorionic twins with weight discordance: a cohort study

Weight discordance is a known risk factor for poor perinatal and neonatal outcomes. However, its impact on growth patterns during childhood remains unclear. This study aimed to examine how weight discordance influences the growth of weight, length, and head circumference during the first 36 months of corrected age (CA), according to chorionicity. A retrospective cohort study of monochorionic and dichorionic twin pairs with weight discordance, born between January 1, 2012, and December 31, 2021, in a tertiary maternity hospital. Weight discordance was considered if there was a difference of more than 20% in estimated fetal weight or birth weight between the twins. z-scores for weight, length, and head circumference at birth and at 1, 6, 12, 18, 24, and 36 months of CA were retrieved, and a longitudinal comparison was performed between monochorionic and dichorionic twin pairs. Two hundred thirty-two infants were included: 64 monochorionic and 168 dichorionic. In monochorionic twins, the differences in weight, length, and head circumference between the smaller and larger co-twins closed six months earlier than in dichorionic twins. Head circumference z-scores became similar six months earlier than length z-scores, and length z-scores became similar six months earlier than weight z-scores. Overall, both small and large monochorionic and dichorionic twins showed increases in all growth parameters during the first 36 months CA, with a more notable increase in smaller monochorionic twins.

Inter-twin weight discordance was observed throughout the growth patterns of both larger and smaller twins. Smaller discordant twins showed adequate catch-up growth, leading to no differences in growth parameters compared to their larger co-twins by 36 months. This study highlights the role of chorionicity in the timing of resolution of growth disparities, with differences among dichorionic twins persisting longer.

• Weight discordance is a known risk factor for poor perinatal and neonatal outcomes, but its effect on childhood growth patterns remains unclear. • Previous studies showed persistent weight and length discrepancies during early childhood, but there is limited data on head circumference and time of growth discrepancy resolution.

• Head circumference z-scores in smaller twins caught up more quickly than length and weight z-scores, suggesting different rates of catch-up growth in different growth parameters. • Growth differences between dichorionic discordant twins persist longer than in monochorionic twins, but by 36 months, no differences remained in any growth parameter.