Trajectories of cognitive development in toddlers with language delays

•In a study of toddlers with early language delays, growth mixture models revealed heterogeneity in cognitive development.•The best-fitting models comprised two nonverbal and three verbal cognitive classes.•Membership in the delayed verbal cognitive trajectory class was related to ASD diagnosis. Toddlers with early language delays (LD) are at risk for developmental difficulties, including autism spectrum disorder (ASD). However, little is known about early cognitive skill acquisition in this population. To explore heterogeneity in cognitive development in toddlers with significant LD (n = 30) or typical development (n = 61), and how this relates to 36-month outcomes (ASD, non-ASD delays, or no delays). Growth mixture modeling of nonverbal and verbal mental age (NVMA, VMA) scores from the Mullen Scales of Early Learning was conducted with data from 18, 24 and 36 months. A two-class NVMA solution was selected (Age Appropriate, 82%, Delayed, 18%); class membership was related to the no delay outcome, and although the proportion of toddlers with ASD in the Age-Expected class was 17% compared to 50% of toddlers with non-ASD delays, this difference was not statistically significant. The best-fitting model for VMA included three classes: Age Appropriate (66%), Delay Catch-Up (23%), Delayed (11%); class assignment differed by outcome. Children in the Delay Catch-Up class were more likely to have non-ASD delays compared to ASD, while the reverse was true in the Delayed class. Cognitive development in toddlers with LD is heterogeneous, and delayed verbal trajectories relate to later ASD diagnosis.