Histometric investigations of placental villi in cases of unexpected fetal acidosis.

It is not unusual that, after an apparently uneventful pregnancy and birth, postpartal analysis of fetal blood unexpectedly reveals the presence of peripartal acidosis, a finding that is inexplicable on the basis of routine observation of the placenta. Using computer-assisted histometric procedures, it is possible to make a quantitative assessment with respect to the maturity and differentiation of villi, thus casting light on the functional anatomy of these structures. 89 single-birth pregnancies were grouped in accordance to the pH of blood in the umbilical artery (pre-acidosis, acidosis, non acidotic). In acidotic newborns, there is an absolute reduction in the surface area of the placenta available for fetomaternal metabolic exchange as well as a reduced surface/weight ratio largely attributable to the significantly reduced villous density. These changes lead to a compensatory increase of epithelial plates on the surface of villi and also causes a decrease in the fetomaternal diffusion distance. The application of a modern computer-assisted structural analysis helps toward clarifying the diagnosis.