Vascular response of the fetal placenta to local occlusion of the maternal placental vasculature.

Local regulation of fetal placental blood flow was studied in 6 near-term sheep. Maternal blood flow was reduced or eliminated to 6-17% of the placenta by ligation or embolization with non-radioactive microspheres. Maternal and fetal placental blood flows were measured, using radioactively-labelled microspheres, before and after vascular occlusion. The change in fetal placental blood flow was significantly different in the occluded as compared to the non-occluded cotyledons. Occlusion of the maternal placental vasculature was associated with a 40% decline in the adjacent fetal placental flow after 24 h. These data support the concept of a local regulatory interaction between fetal and maternal placental circulations wherein fetal placental blood flow is dependent upon the adjacent maternal flow.