Scanning electron microscopy of human placental villi from early and late in gestation.

Human placental villi from term placentas and from 10 to 14 week placentas were examined in the scanning electron microscope (SEM) after critical point drying. When prepared by this method, the syncytial surface appears covered with slender microvilli similar to those seen in transmission electron micrographs. We find no support in our observations for the suggestion that the trophoblastic surface is a mosaic of microvillous and nonmicrovillous areas or that substantial areas lack microvilli. In addition, the villi often show circumferentially oriented furrows. SEM's of the early placentas showed numerous syncytial sprouts, most of which represent stages in the formation of new free or terminal villi.