THE ORIGIN AND EFFECTS OF PROTEINURIA IN PREGNANCY*

Abstract

SummaryThe proteinuria of nephrotic syndrome in pregnancy and pre‐eclampsia was investigated by immunochemical techniques that enabled identification of individual proteins and estimated the renal clearance of proteins, and hence the selectivity of the proteinuria. It has been shown that the proteinuria of pre‐eclampsia is a result of a leak through a damaged glomerular basement membrane with no apparent tubular cause for protein loss.The differential protein clearance in pre‐eclampsia does not suggest that this will be a promising method for distinguishing pre‐eclamptic nephropathy from most cases of chronic glomerulonephritis, but the proteinuria of pre‐eclampsia does show some similarities to that in renal vein thrombosis. This suggests that the deposition of fibrinoid material in the glomerular basement membrane is the probable cause of proteinuria in pre‐eclampsia.The heavy urinary protein loss in pre‐eclampsia produces hypogammaglobulin‐aemia in the fetus. A fall in serum albumin, transferrin and IgG, with an elevation of alpha2‐macroglobulin and β‐lipoprotein is found in the mother. These maternal protein changes are identical to those occurring in nephrotic syndrome and are a result of “molecular sieving” of proteins of intermediate molecular weight through the damaged basement membrane.It is postulated that these serum protein changes are in part responsible for some of the clinical complications of both conditions, and that a rise in the level of the two macroglobulins may, by their antiplasmin activity, exacerbate disseminated intervascular coagulation and deposition of fibrin within the kidneys of a patient with pre‐eclampsia.