Comparison of factors contributing to developmental attainment of children between 9 and 18 months.

Background: Little is known about how contributing factors of development change during early childhood in Japan. The aim of this study was to investigate the factors that contributed to the developmental attainment of children between 9 and 18 months of age using prospective longitudinal data from a developmental cohort study.

Methods: We used data from observations at 3 time points (at infant age of 4, 9 and 18 months) in the Japan Children's Study. Mothers were administered questionnaires that requested information about their child's perinatal outcomes, temperament, family structure, family income, parental education, parenting stress, and child-rearing environment at home. At 9 and 18 months, mothers completed the Kinder Infant Development Scale to evaluate their child's development.

Results: A total of 284 children were available for analysis. Female children and children having siblings had higher probability of attaining developmental norms at 18 months than male and only children. Birth weight, gestational age, and temperament were associated with development at 9 months, but the effects of gestational age and temperament on development disappeared at 18 months. Stimulation from the mother at 9 months was not only related to development at that age but also promoted development at 18 months.

Conclusions: Our findings suggest that the role of family environmental factors such as early mother's stimulation and sibling's existence in development during early childhood might become more important as the child gets older.