The Changing Number of Cells in the Human Fetal Forebrain and its Subdivisions: A Stereological Analysis

The total number of cells – including both neurons and glial cells – was estimated in the neocortical part of the human fetal telencephalon in 22 normal brains within four major developmental zones: the cortical plate/marginal zone, the subplate, the intermediate zone and the ventricular/subventricular zone. The fetal ages ranged from 13 to 41 weeks of gestation. The cellular growth in the human fetal forebrain appears to be two-phased: one rapid, exponential phase from 13 to 20 weeks of gestation and a second and slower phase, which increases linearly, from approximately 22 weeks of gestation to term. From 13 to 20 weeks of gestation the total number of cells increases by a factor of 4.3 from 3 × 10 9 cells to 13 × 10 9 cells at 20 weeks of gestation. From mid-gestation to term, the total cell number increases by a factor of 2.9 to 38 × 10 9 cells in the newborn infant. Studying cellular growth in the normal human fetal brain is important since it may serve as a useful parameter for the assessment of cortical growth in non-invasive and histological studies, and thus improve the analysis of fetal brain disturbances.