Placental basal plate formation is associated with fibrin deposition in decidual veins at sites of trophoblast cell invasion

OBJECTIVE: We hypothesize that placenta growth and basal plate (Nitabuch's fibrinoid) formation involves fibrin deposition in decidual veins as trophoblast cells invade. STUDY DESIGN: Decidua from women who underwent first trimester elective pregnancy termination (n = 15 women), in situ pregnancy (n = 2 women), and ectopic pregnancy (n = 5 women) were immunostained with polyclonal antibodies to fibrin. Serial sections of decidua were studied with monoclonal antibodies to oncofetal fibronectin, cytokeratin, and Factor VIII-related antigen. RESULTS: In all intrauterine pregnancies, trophoblast cells were identified with clots in decidual veins. Fibrin and oncofetal fibronectin were present in veins at sites of trophoblast cell invasion and in the developing basal plate matrix where villi had implanted into veins. Fibrin deposits were not seen in decidual parietalis of ectopic or in situ pregnancies. CONCLUSION: We have identified fibrin in decidual veins that is associated with trophoblast cell invasion. We speculate that the formation of basal plate protein (Nitabuch's fibrinoid) involves these intravenous fibrin deposits.