Complex Trajectories of Brain Development in the Healthy Human Fetus

TLDR

Brain asymmetry evolves throughout the human life span. The study characterizes global and hemispheric brain growth in healthy human fetuses during the second half of pregnancy with 3‑D MRI. The authors performed 3‑D MRI on 166 healthy fetuses (18–39 weeks), reconstructed brain volumes for cortical gray matter, white matter, deep subcortical structures, and cerebellum, and quantified growth rates and hemispheric patterns. During the second half of gestation, all brain regions expanded markedly—cerebellum 34‑fold, white matter 22‑fold, cortical gray matter 21‑fold, deep subcortical structures 10‑fold—with early hemispheric asymmetries that equalize by term, demonstrating that 3‑D MRI can noninvasively quantify fetal brain asymmetry.

Abstract

This study characterizes global and hemispheric brain growth in healthy human fetuses during the second half of pregnancy using three-dimensional MRI techniques. We studied 166 healthy fetuses that underwent MRI between 18 and 39 completed weeks gestation. We created three-dimensional high-resolution reconstructions of the brain and calculated volumes for left and right cortical gray matter (CGM), fetal white matter (FWM), deep subcortical structures (DSS), and the cerebellum. We calculated the rate of growth for each tissue class according to gestational age and described patterns of hemispheric growth. Each brain region demonstrated major increases in volume during the second half of gestation, the most pronounced being the cerebellum (34-fold), followed by FWM (22-fold), CGM (21-fold), and DSS (10-fold). The left cerebellar hemisphere, CGM, and DSS had larger volumes early in gestation, but these equalized by term. It has been increasingly recognized that brain asymmetry evolves throughout the human life span. Advanced quantitative MRI provides noninvasive measurements of early structural asymmetry between the left and right fetal brain that may inform functional and behavioral laterality differences seen in children and young adulthood.