Shunting the intervillous space: new concepts in human uteroplacental vascularization.

Objective: It is supposed that the intervillous space is not perfused by maternal blood during the first trimester, suggesting vascular shunts in the myometrium. We therefore attempted to provide arguments for a functional vascular anastomotic network located in the placental bed during human pregnancy.
Study Design: Three-dimensional (3D) sonography, laboratory analyses, and anatomic studies (hysterectomy specimens, uteroplacental vascular cast) were performed.
Results: Color Doppler showed a vascular network with anastomotic aspect located in the placental bed. A vascular cast of a uterus, obtained after postpartum hemorrhage, demonstrated a vascular anastomotic network in the myometrium. Higher PO2 levels in the uterine vein compared with the intervillous space confirmed the functional nature of this shunt. Low resistances in the uterine arteries during the first week after delivery suggested that this vascular network remains functional after placental expulsion.
Conclusion: Our studies have yielded functional and anatomic evidence of an arteriovenous shunt located in the subplacental myometrium.