An electron microscopic study of fetal capillary basal laminas of "normal" human term placentas.

Electron microscopic examination of terminal (free-floating) villi of definable normal human term placentas emphasizes the variable fine structural appearance of the fetal capillary basal lamina (FL). The FL assumes both a unilaminar and multilamellar configuration in each placenta examined; the multilamellar portions are usually composed of individual layers which tend to branch and anastomose. The constant indentification of collagen fibrillar profiles between these electron-dense layers argues against the notion that the multilamellar portions of the FL arise via a simple splitting or disaggregation of pre-existing unilaminar FL's.