Stereology and the placenta: where's the point? -- a review.

The value of stereology for describing the three-dimensional (3D) structural composition and spatial arrangement of biological specimens from essentially two-dimensional (2D) thin sections is indisputable. By allowing economical quantitation of microscopical sections, stereology facilitates interpretations of normal and perturbed structure from the whole organ down to the subcellular levels. It incorporates the essential features of all sound study designs: (i) randomised sampling which is efficient and unbiased, and (ii) estimation tools which are simple, precise and unbiased or minimally biased. With these sampling and estimation tools, stereology offers a sure and safe option for characterising the total volumes, surfaces and lengths of placental compartments, the total numbers and mean sizes of nuclei or cells, and the spatial arrangements of tissues or intracellular ingredients. This review identifies the basic features of the stereological approach before indicating several ways in which stereology has been used to aid the description and interpretation of placental functional morphology from the whole organ to the molecular level. Examples include diffusive transport, villous growth, fetoplacental angiogenesis, trophoblast turnover, arterial vascular remodelling and high-resolution immuno-localization studies.