Are intervillous (between villi) thrombi and intervillous fibrin maternal or fetal malperfusion lesions?

Intervillous Thrombus and Intervillous Fibrin Classification

Intervillous thrombi and intervillous fibrin are classified as maternal vascular malperfusion (MVM) lesions, not fetal malperfusion lesions. 1, 2

Pathophysiologic Basis

These lesions reflect abnormalities in the maternal intervillous space circulation and oxygenation dynamics:

• Intervillous fibrin deposition occurs within the maternal blood space between placental villi, representing altered flow dynamics and coagulation in the maternal circulation perfusing the placenta 2

• Intervillous thrombi similarly form in the maternal intervillous space and are explicitly categorized as maternal vascular malperfusion findings 1, 3

• Both lesions indicate problems with maternal blood flow and oxygenation in the intervillous space, which is filled with maternal blood that bathes the fetal villi 2

Clinical Context and Associated Findings

MVM lesions including intervillous fibrin and thrombi are commonly found alongside other maternal malperfusion pathology:

• Frequently co-occur with decidual vasculopathy, infarction, and abnormal spiral artery remodeling 1, 2

• Associated with fetal growth restriction when present, particularly when multiple MVM lesions coexist 3, 4

• Increased perivillous fibrin is specifically documented as occurring with basal plate myometrial fibers (a maternal malperfusion finding) 1

Distinction from Fetal Malperfusion

Fetal vascular malperfusion involves completely different pathology:

• FVM lesions include umbilical cord obstruction, fetal thrombotic vasculopathy, and villous stromal-vascular abnormalities affecting fetal vessels within the villi 5

• FVM reflects reduced or absent perfusion of villous parenchyma by the fetus through the umbilical cord circulation 5

• The intervillous space is a maternal blood compartment, not part of the fetal circulation 2

Common Pitfall

Do not confuse the location: intervillous (between villi, in maternal blood space) versus intravillous (within villi, involving fetal vessels). Intervillous pathology is maternal; intravillous pathology is fetal 2