Total Cell Number in Fetal Brain

In this study the material comprises brains from three aborted fetuses and two fullterm infants who died at birth. The gestational ages ranged from the 22nd week to term. All cases were without malformations, known chromosomal abnormality, hydrops, and systemic infections, and all had normal birth weights with fetal growth indices (observed birth weight/expected mean birth weight) between 0.9 1.05. The preliminary results show a five fold increase in the total cell population in the marginal zone/cortical plate, MZ/CP (future neocortex), from week 22 until term. In the transient subplate zone, SP, the total cell number was more than doubled from week 22 to week 30-35, and then decreased towards term. In the intermediate zone, IZ (future white matter), the total cell population was doubled from week 22 until term. The total cell number in the ventricular/subventricular zone, VZ/SZ (germinal matrix), was reduced by a factor of five from week 22 until term. A histological differentiation between neurons and glial cells was not possible. The optical fractionator was used to estimate the total cell population in four characteristic developmental zones in the human fetal brain. Fetal brain tissue undergoes considerable and rather unpredictable shrinkage during fixation. However, using the fractionator principle it is possible to eliminate this problem, provided that the structure of interest (one brain hemisphere) is fully intact.