The development of the placental villus during normal pregnancy: morphometric data base.

The morphological structures of the terminal villus of the normal human placenta were evaluated morphometrically throughout pregnancy. The Videoplan (Kontron) system was used to measure a total of 6000 villi. The cross-sectional surface and circumference of the villus decrease continuously until the 28th week and remain stable thereafter. The cross-sectional surface, number, and circumference of villous vessels only increase until the 20th week. The relative degree of vascularization, however, increases further until 28th week together with a continuous decrease in villous size. Epithelial plates start to appear in the 18th to 20th week, and their development is essentially completed by the 28th week. According to the data presented, the development and differentiation of the placental villus are completed by the 28th week of gestation. Any further increase in nutritional capacity can only be provided by an increase in the number of villi and not their individual maturation. These results represent a morphometric data base for the quantification of retarded placental development in placental insufficiency.