The distribution of microvilli over the villous surface of the normal human term placenta is homogenous.

The study was carried out to estimate stereologically whether regional differences exist in the distribution of microvilli between vasculo-syncytial (VSM) and non-vasculo-syncytial (non-VSM) areas of the villous surface in normal term placenta. In ten placentae a normal lobe was perfusion-fixed at a pressure of 60 mm Hg, and the intervillous space was perfused at 10 mm Hg. The tissue was routinely processed for ultrastructural examination. Stereological estimates relating to the length and diameter of microvilli, and to the villous surface amplification factor in adjacent but contrasting (VSM and non-VSM) regions, were obtained. A paired "t' test showed no significant difference in the villous surface amplification factor between the two regions (5.18 +/- 0.54 and 5.22 +/- 0.54 respectively, mean +/- s.e.m. P > 0.05). In addition, there were no significant differences between the length and diameter of microvilli in both regions (P > 0.05 in both). The results confirm that the normal term placenta has a continuous and even covering of microvilli over the syncytium.