Stereology and its impact on our understanding of human placental functional morphology.

The new stereology permits the objective, quantitative description of morphology by efficient and design-based methods. Applications to placentas in normal and abnormal pregnancies have proved of great value for challenging earlier misconceptions and interpreting better the processes of growth, morphogenesis, adaptation, and functioning at the whole-organ level. This contribution reviews the essential features of the stereological approach, identifies useful structural quantities, and provides examples of their application in various experiments of nature. We focus particularly on normal gestation and the effects of pregnancies associated with high altitude, maternal diabetes mellitus, preeclampsia, and maternal smoking.