Abstract
BACKGROUND: 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. AIMS: 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). METHODS: 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. RESULTS: 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. CONCLUSIONS: Cognitive development in toddlers with LD is heterogeneous, and delayed verbal trajectories relate to later ASD diagnosis.