RESUMEN
Studies on 20 placentae; 5 placentae after normal pregnancy and delivery; and 15 placentae after normal pregnancy and post-term delivery [after 42 weeks] have been carried out. Electron microscopic sections have been prepared for ultrastructure study of placental tissue. Histological study of post-term placental tissue showed dilated cisternae of rough endoplasmic reticulum [rER], swollen mitochondria, calcium deposition and decrease in cell membrane microvilli. Collagen deposition increased in chorion and thickening of the wall of blood vessels was observed. The reticular layer was disrupted. We conclude that the microscopic changes in the post-term placenta can produce placental insufficiency in post-term .foetus due to decrease in the capacity of trophoblast cells to exchange the maternal blood and foetal blood