Subinvolution of the uteroplacental arteries: an immunohistochemical study

Subinvolution of uteroplacental arteries is a well-recognized cause of hemorrhage in the postpartum period. Although the physiological changes in these arteries during pregnancy are well documented, the sequence of events in normal involution is largely unknown. A recent immunohistochemical study has raised the possibility of an abnormal interaction between maternal uterine cells and fetal trophoblast in subinvolution. An indirect immunoperoxidase technique was used to compare deposition of complement components and immunoglobulin in subinvoluted and normally involuted uteroplacental arteries in 25 cases of postpartum hemorrhage. Deposits of C1q, C3d, C4, and C9 were detected within the walls of normally involuted vessels, whereas deposition of C1q, C3d, and C4 was absent in subinvoluted vessels; C9 was detected only focally. Deposition of immunoglobulins G, A, and M mirrored those described for complement components. The results suggest that immunological factors are necessary for the process of normal involution of uteroplacental arteries and are deficient in subinvoluted vessels.