Developmental milestones during the first three years as precursors of adult intelligence.

Abstract

Few studies have investigated associations of milestone development in early childhood with intelligence in adulthood in typically developing children. The current study is an extension of 2 previous studies on smaller samples and investigated associations of age at attainment of 32 developmental milestones attained between 0 and 3 years of age with adult intelligence and explored whether the effects of early infant milestones are mediated through later development during subsequent years. Mothers of 8,400 children from the Copenhagen Perinatal Cohort recorded 32 developmental milestones during the child's first 3 years of life. Information on at least 1 developmental milestone was available for 2 subsamples with adult follow-up information on intelligence: Børge Priens Prøve (BPP) was available for 2,567 men while Wechsler Adult Intelligence Scale (WAIS) was available for 1,000 men and women. The study found that early attainment of milestones, primarily those related to standing/walking and language development, was associated with higher intelligence in adulthood. The adjusted BPP means were 103.7, 101.7, and 99.5, respectively, for being able to name objects/animals in pictures at less than 18 months, 18-24 months, and later than 24 months. Mediation analyses showed direct associations of the 1-year milestones related to standing/walking with intelligence with the direct association accounting for 74.6% and 64.4% of the total association in each subsample. Thus, milestones related to standing and walking primarily show a direct association with adult intelligence and are to a smaller extent mediated by milestones reflecting development during the subsequent years, in particular language development. (PsycINFO Database Record

Language development and intelligence in midlife

“…Three previous longitudinal studies are based on a study design in which cognitive outcomes are measured in adulthood or adolescence: Two of these studies are based on the same birth cohort as the present study, and one study used the BPP as outcome completed at a mean follow‐up age of 19.3 years (Flensborg‐Madsen & Mortensen, ), while the other used WAIS administered at a mean adult age of 27.6 years (Flensborg‐Madsen & Mortensen, ). The studies investigated the timing of 20 developmental milestones assessed during the age from one to three years within the areas of language, walking, eating, dressing, social interaction, and toilet training, and associations were, also in these studies, analysed by multiple linear regressions adjusting for potential confounding factors.…”

“…Although two similar subtests are included in both the BPP and the I‐S‐T 2000 R, these tests are not directly comparable, and the WAIS is a much more comprehensive measure of intelligence than the other test. However, comparison of the standardized regressions coefficients suggests that the coefficients for midlife intelligence may be at least as high as those for the BPP (Flensborg‐Madsen & Mortensen, ), while the coefficients for the WAIS may be slightly higher (Flensborg‐Madsen & Mortensen, ). Thus, it may be cautiously concluded that the present study provides no evidence that the influence of early language development is diluted over the adult life course.…”

“…At a 3‐year CPC follow‐up assessment, the mothers were interviewed and asked to retrospectively recall the child's age at attaining 20 developmental milestones. The milestones covered a wide range of behaviours, but milestones related to language and social interaction were chosen to be the main focus of the present study because they have shown the most robust associations with intelligence in young adulthood (Flensborg‐Madsen & Mortensen, , ) and because milestones related to the other areas were not significantly associated with midlife IQ (Table S2). Table includes a description of the included milestones and presents median age at attainment and the 25% and 75% percentiles of each milestone.…”

“…In two previous studies based on the Copenhagen Perinatal Cohort (CPC), the relationship between the timing of early milestones and intelligence in young adulthood was addressed by examining associations between 20 developmental milestones (including language milestones) attained within the ages of one to three years and intelligence assessed by the Børge Prien's Prøve (BPP) (Teasdale, ) and the Wechsler Adult Intelligence Scale (WAIS) (Wechsler, ) in adulthood at mean ages of 19.3 and 27.6 years, respectively (Flensborg‐Madsen & Mortensen, , ). Several significant associations between the timing of milestones and intelligence were discovered, with the largest associations generally found for milestones related to language and social interaction; the latter primarily including milestones reflecting social aspects of language and communication.…”

Early life predictors of intelligence in young adulthood and middle age

“…Postnatal factors of importance for later intelligence have included breastfeeding [14,15], institutional care [16], and physical growth of the child, especially in the first year [17]. Finally, early developmental milestones have been documented in several studies to be associated with adult IQ [18,19]. The levels of significance and strength of these early life factors vary across studies which may reflect study differences in the included predictors and covariates as well differences between study samples.…”