Original articleDo developmental milestones at 4, 8, 12 and 24 months predict IQ at 5-6 years old? Results of the EDEN mother-child cohort

•Children who had not reached a milestone acquired by 90% of the children of the same age scored.•2.5 IQ points lower when milestones were assessed at 4 and 8 months.•5 IQ points lower when assessed at 12 months.•8 IQ points lower when assessed at 24 months.•Early milestones in the language domain were those that best predict intelligence at 5-6 years old.

RationaleThe present study aims: (i) to determine how well developmental milestones at 4, 8, 12 and 24 months may predict IQ at 5-6 years old, (ii) to identify cognitive domains during the first two years that best predict later IQ and (iii) to determine whether children with IQ in the normal range at 5-6 years old may differ from disabled (IQ < 70) and gifted children (IQ > 130) with regard to their early cognitive development.MethodThe main developmental milestones were collected through self-administered questionnaires rated by parents at 4, 8, 12 and 24 months and through parental questionnaires administered by a trained interviewer and questionnaires completed following a medical examination at 12 months. These questionnaires were derived from the Brunet-Lézine Psychomotor Development Scale and they addressed several cognitive domains (gross and fine motor skills, language and socialization).Results(i) Developmental milestones predict a substantial part of the later IQ variance from 24 months (R2 ∼ 20%). (ii) Early language skills more strongly predict later IQ than the other cognitive domains. (iii) Several cognitive domains, but particularly language skills, predict disabled children at 5-6 years old (from the age of 8 months) and gifted children (from the age of 12 months).DiscussionThe present study provides valuable information for early developmental assessment and could contribute to a better understanding of intellectual development.