Renal disorders in pregnancy

Renal disorders in pregnancy are common. In high income countries, approximately 3% of pregnant women have chronic kidney disease (CKD) and often it is recognized for the first time during pregnancy. Approximately one fifth pregnant women developing preeclampsia before 30 weeks’ gestation have previously undiagnosed CKD, especially those with severe proteinuria. Defining and staging CKD in pregnancy is challenging: from one hand physiological hyperfiltration might significantly alter CKD staging. On the other hand, the application of equations for estimating glomerular filtration rate (GFR) is strongly discouraged during pregnancy. By analyzing data from the literature, it is reasonable to assume that serum creatinine and albuminuria should be considered the most appropriate tests both for diagnosing and monitoring pregnant women with CKD. Creatinine clearance is cumbersome and the collection of the 24-h urine sample is often inaccurate, while proteinuria is affected by several analytical pitfalls. Serum creatinine should be measured by traceable methods in order to make comparable results between different laboratories. Albuminuria can be screened by dipstick methods; however, any positive result must be confirmed by a quantitative measurement either on a 24-h urine sample or on a first morning urine sample, reporting results as albuminuria-to-creatininuria ratio. Nephelometric methods for albuminuria enable an accurate measurement even in a range of 5–15 mg/L. Any negative dipstick result must be carefully evaluated on the basis of history and clinical signs, tacking into account possible false negative results due to the presence of a protein mixture constituted either by a very low concentration of albumin or by globular proteins only. Cystatin C should be used in the first trimester to predict the risk of preeclampsia and that of gestational diabetes mellitus. Finally, pregnant women with proteinuria must be periodically checked for urinary tract infection (UTI) by urine cultures.