Early intervention can reduce disability in children diagnosed with autism spectrum disorder. Screening for autism spectrum disorder in young children identifies those at increased likelihood of diagnosis who may need further support. This study assessed in "utero" exposure to maternal obesity and diabetes and offspring performance on the Quantitative Checklist for Autism in Toddlers, an autism spectrum disorder screening questionnaire administered between 18 and 24 months at well-child visits. This retrospective cohort study included 65,433 singletons born in a single healthcare system. Demographic data, maternal obesity, Type 1/Type 2 and gestational diabetes mellitus information, and Quantitative Checklist for Autism in Toddlers score in children 12-30 months old were extracted from electronic medical records. Negative binomial models were used to estimate incidence rate ratios of associations between maternal obesity and diabetes exposure and continuous offspring Quantitative Checklist for Autism in Toddlers scores. Maternal obesity, Type 1/Type 2 diabetes (incidence rate ratio: 1.13, 1.06-1.21) and gestational diabetes mellitus [less than or equal to] 26 weeks (incidence rate ratio: 1.10, 1.05-1.17) were associated with one-unit increases in Quantitative Checklist for Autism in Toddlers scores. Relationships with obesity and gestational diabetes mellitus [less than or equal to] 26 weeks remained after mutual adjustment and excluding children with autism spectrum disorder diagnoses. No associations were reported for gestational diabetes mellitus > 26 weeks. Maternal obesity and diabetes were associated with higher Quantitative Checklist for Autism in Toddlers scores in children 12-30 months old, suggesting these exposures in pregnancy may be associated with a range of early childhood behavior.