Monochorionic placenta

Feto–fetal transfusion syndrome. THE MONOCHORIONIC PLACENTA

FFTS always develops from a monochorionic placenta which bears several intertwin vascular connections of different types on the chorionic plate. These transplacental communications were first described in 1687 but their role was not suspected until 1882, when Schatz described the ‘third circulation’ and individualized all possible patterns of anastomoses Robertson and Benirschke using large ex-vivo placental dye injection studies refined the close relation between placental anastomoses and monochorionic placentation and described the proportions of different types of sharing vessels.

Vascular anastomoses are of three histological types: namely, artery-to-artery (AA), arteryto-vein (AV or VA), and vein-to-vein (VV) anastomoses. AA and VV are bidirectional and superficial anastomoses that indirectly connect the two fetal umbilical cords. These vessels run entirely, without interruption, on the surface of the chorionic plate. In contrast, AV and VA are deep anastomoses that always mediate a unidirectional blood flow AA and AV are the most frequent anastomoses (80% and 75%, respectively), unlike VV which are only present in 15% of monochorionic placentas. The specific role of each type of anastomosis in the development or non development of FFTS is controversial.


Some studies correlate the development of FFTS with a paucity of superficial anastomoses Recently, Wee et al using placental vascular casting, described another type of AV. These atypical deep AV anastomoses could be found in up to 90% of monochorionic placentas and could not be individualized either by endoscopy or dye injection. The possibility of cast artifacts makes it controversial. The paucity of and imbalance between the unidirectional (AV) and the bidirectional (AA or VV) are likely to influence the underlying pathophysiology.

The most commonly shared hypothesis is that FFTS develops when there is no effective means for AV blood to return from recipients to donors.