Timing and trajectories of fetal growth related to cognitive development in childhood.

The authors investigated timing and trajectories of fetal growth in relation to childhood development in the National Institute of Child Health and Human Development-Scandinavian Study of Successive Small-for-Gestational Age Births (1986-1988) (n = 1,059). Fetal size was assessed by ultrasound at 17, 25, and 33 gestational weeks and at birth. Bayley Scales of Infant Development and the Wechsler Preschool and Primary Scale of Intelligence-Revised tests were conducted at ages 1 and 5 years, respectively, producing mental and psychomotor development indexes and verbal and performance intelligence quotients. Relative fetal size was calculated as a standard deviation score at each data point; growth trajectories were explored with longitudinal mixture models. Fetal size at 17, 25, and 33 weeks was positively associated with mental development index; larger size at 33 weeks and at birth was associated with higher verbal intelligence quotient scores (2.61, 95% confidence interval: 1.06, 4.15 and 1.90, 95% confidence interval: 0.67, 3.13 increase per 1 standard deviation score, respectively); findings were similar for performance intelligence quotient. Seven trajectories were identified; scores were lower for "small" and "medium-to-small" trajectories than for "medium" and "big" (representing normal size) trajectories: mental development index (P < 0.01), performance intelligence quotient (P < 0.001), and verbal intelligence quotient (P < 0.001). Overall, larger fetal size in the second and third trimesters was positively associated with childhood development. Fetal growth trajectories may matter beyond birth.