Figure 2.

Development of the placental vasculature. (A) Placental villi of 6 weeks gestational age prior to onset of the chorionic circulation, showing the presence of nucleated erythrocytes in the developing fetal capillaries (arrowed). (B) Villi at 14 weeks gestational age showing the presence of non-nucleated erythrocytes in the larger vessels within the stromal core, indicative of onset of the chorionic circulation. (C) Villi of 27 weeks gestational age. By now the smaller peripheral villi are being elaborated. (D) Villi of 40 weeks gestational age showing well vascularized terminal villi. Scale bar for all images = 50 μm. Stain; haematoxylin and eosin for all.