What is known:
• Younger age at attainment of motor developmental milestones positively predicts cognitive outcomes in adulthood.
• Both pre- and postnatal factors have been associated with age of attaining milestones in infancy.
What is new:
• First study to provide a systematic evaluation of a broad selection of predictors of infant milestone attainment.
• Variables within the domain of Pregnancy and delivery, especially gestational age and birth weight, explained the largest proportion of variance in milestone attainment.
• The variance explained by the predictors decreased time-dependently with later milestones.