Growth trajectories and intellectual abilities in young adulthood: The Helsinki Birth Cohort study.

Slow childhood growth is associated with poorer intellectual ability. The critical periods of growth remain uncertain. Among 2,786 Finnish male military conscripts (1952-1972) born in 1934-1944, the authors tested how specific growth periods from birth to age 20 years predicted verbal, visuospatial, and arithmetic abilities at age 20. Small head circumference at birth predicted poorer verbal, visuospatial, and arithmetic abilities. The latter 2 measures were also associated with lower weight and body mass index (weight (kg)/height (m)(2)) at birth (for a 1-standard-deviation (SD) decrease in test score per SD decrease in body size > or = 0.05, P's < 0.04). Slow linear growth and weight gain between birth and age 6 months, between ages 6 months and 2 years, or both predicted poorer performance on all 3 tests (for a 1-SD decrease in test score per SD decrease in growth > or = 0.05, P's < 0.03). Reduced linear growth between ages 2 and 7 years predicted worse verbal ability, and between age 11 years and conscription it predicted worse performance on all 3 tests. Prenatal brain growth and linear growth up to 2 years after birth form a first critical period for intellectual development. There is a second critical period, specific for verbal development, between ages 2 and 7 years and a third critical period for all 3 tested outcomes during adolescence.