There are several possible reasons why women develop proteinuria during pregnancy: 1. Because women have problems with their kidney function. Under normal circumstances, protein will not appear in the urine of normal women during pregnancy because the molecular mass of protein is relatively large and cannot pass through the filtration membrane of the glomerulus. But when there is a disease in the kidney, the most common disease is glomerulonephritis, which can lead to an increase in the permeability of the filtration membrane of the glomerulus, thus leading to the appearance of protein in the urine. During pregnancy, women are prone to external bacterial infections due to the relatively poor immunity of the body, which also makes them prone to acute glomerulonephritis, thus leading to the appearance of protein in the urine. 2. It may be a normal physiological condition. Because some women experience transient proteinuria during pregnancy, it can be considered normal to have protein in the urine occasionally. But the amount should not be too much and should not appear often, for this situation does not need to be treated.