The study attempted to correlate to several anatomic and biochemical parameters of the human placenta. The area and diameter of terminal villi, and the area and height of the syncytiotrophoblast were assessed. The trophoblastic activity of succinate dehydrogenase, an enzyme conditioning the function of mitochondrial electron transport chain, was measured densitometrically. The central and peripheral portions of the placenta were studied with respect to their morphological differences. The study has shown that changes in the morphometric parameters of terminal villi and in succinate dehydrogenase (SDH) activity tend to follow a stable 12-hour rhythm with morning and evening maxima. We observed phasic differences in SDH activity and the height of syncytiotrophoblast between central and peripheral terminal villi, which indicates the existence of an intrinsic mechanism integrating the function of the placenta. It seems that the circadian fluctuations in the structure and activity of the placenta and consequent fluctuations in substrate exchange between the mother and children could be an important consideration in clinical practice.

Keywords: Circadian Rhythm, Placenta, morphometry, syncytiotrophoblast, Succinate Dehydrogenase