Early lexical development and risk of verbal and nonverbal cognitive delay at school age

To characterise the relationship between preschool lexical delay and language comprehension and nonverbal intelligence at school age.

The mothers of 2724 children completed the MacArthur Communicative Development Inventory when their child reached 1.5 years and the Language Development Survey and the Parent Report of Children's Ability at 2.5 years. When the children were 6 years old, we assessed vocabulary comprehension and nonverbal intelligence using Dutch batteries for language and nonverbal intelligence.

Demographic factors explained 9.9% of the variance in vocabulary comprehension and 8.7% of the variance in nonverbal intelligence at 6 years. Male gender, low maternal education and non-Western ethnic background predicted vocabulary comprehension delay at 6 years. Lexical development at 1.5 and 2.5 years explained only 3.8% of the variance in language comprehension at the age of six. Late onset expressive vocabulary delay increased the risk of language comprehension and nonverbal intelligence delay at 6 years (OR=2.31, 95% CI: 1.62-3.29 and OR=1.74, 95% CI: 1.17-2.58, respectively).

Sociodemographic factors are important predictors of delays in language and nonverbal abilities as children enter school. In contrast, early expressive lexical delays, in particular before the age of two, have limited predictive power for language delays at the age of six.