This paper focuses on the aspects of the lexicon in 66 prematurely born very-low-birth-weight and 87 full-term Finnish children at 2;0, studied using the Finnish version of the MacArthur Communicative Developmental Inventory. The groups did not differ in vocabulary size. Furthermore, the female advantage in vocabulary size was not seen in preterm children. The overall shapes of the trajectories for the main lexical categories as a function of vocabulary size were highly similar in both groups and followed those described in the literature. However, there were significant differences in the percentage of nouns and grammatical function words between the two groups. The results suggest that prematurity ‘cuts off’ the female advantage in vocabulary development. Furthermore, it also seems that there are differences between prematurely born and full-term children in the composition of the lexicon at 2;0. The findings support the universal sequence in the development of lexical categories.

This study suggests that maternal depression may be a risk factor in the development of the mother-infant relationship between preterm infants and their mothers. Therefore, it would be important to identify signs of depression in mothers of preterm infants to offer early support.

The growth rate and the development of the composition of the receptive and expressive lexicon were studied in a longitudinal sample of 35 Finnish children. The MacArthur Communicative Development Inventory was used to gather data of the receptive lexicon at 0;9, 1;0 and 1;3, and the expressive lexicon at 0;9, 1;0, 1;3, 1;6 and 2;0. The receptive lexicon was acquired earlier, at a faster rate and with higher individual variation than the expressive lexicon. A gender difference was found in expressive vocabulary, but not in receptive vocabulary. The growth trajectories of semantic lexical categories detected in both lexicons resembled each other. Verbs were acquired more readily in receptive lexicons. Results support a universal sequence in the development of the composition of the lexicon.