Natural history of chronic proteinuria complicating pregnancy.

OBJECTIVE: Although the significance of proteinuria is well-documented for pregnancy complicated by preeclampsia or diabetes, protein excretion of up to 300 mg per day is considered normal for uncomplicated pregnancy. Our purpose was to determine the significance of otherwise "asymptomatic" proteinuria identified during pregnancy.

STUDY DESIGN: We reviewed the perinatal outcome of 65 pregnancies in 53 women with the following criteria: (1) proteinuria exceeding 500 mg per day, (2) no previously known renal disease, (3) no reversible renal dysfunction, and (4) no evidence for preeclampsia at discovery.

RESULTS: Renal insufficiency coexisted in 62% of women, and 40% had chronic hypertension. Excluding 8 abortions, 53 (93%) of 57 pregnancies resulted in live infants; 45% of infants were delivered preterm and 23% had growth retardation. Of these 57 women, 62% demonstrated clinical evidence compatible with superimposed preeclampsia, and although the incidence of preeclampsia was increased with isolated proteinuria (29%), it was increased even more when there was associated chronic hypertension (incidence 100%) or renal insufficiency (incidence 58%). All 21 women who eventually underwent renal biopsy had histologic evidence of renal disease. To date, with only a limited follow-up of these 53 women, 11 (20%) have progressed to end-stage renal disease.

CONCLUSION: "Asymptomatic" proteinuria is associated with a number of adverse pregnancy outcomes and serious long-term maternal morbidity.