Early childhood weight trajectory differences in twins, singletons, and gestational-age matched singletons.

Objective: Understanding of twin growth in the United States (US) is based on outdated or predominantly non-Hispanic White samples, and the age at which twins catch up to singletons is unclear. In this study, we characterized normative weight trajectories of twins and singletons in a contemporary, diverse cohort. Methods: Data were from the PROMISE study, an electronic health record-based cohort of pregnant people and their children in the US (2005-2021). The Jenss model was used to characterize weight trajectories from 0 to 24 months of age. Twins ( Results: Male and female twins had lower birth weight compared to singletons and experienced a high rate of weight gain throughout infancy. Among males, twins caught up in weight to the full singleton cohort and to GA-matched singletons at approximately 12 and 6 months, respectively. Among females, twins caught up to GA-matched singletons at approximately 15 months but did not fully overcome their birth weight disadvantage to the full singleton sample by 24 months. Conclusions: These findings highlight that the use of singleton growth charts or preterm singleton growth charts among twins may be inappropriate and suggest the need for a twin-specific growth chart. Future research is needed to understand factors that drive differences in weight trajectories between twins and singletons and to guide twin-specific guidelines.