Preeclampsia is a serious pregnancy complication characterized by new onset of high blood pressure, often with protein in the urine or other signs of organ damage. It usually develops after 20 weeks of pregnancy in individuals whose blood pressure was previously normal. If unmanaged, it can lead to severe health concerns for both the pregnant individual and the baby, affecting various organ systems, including the kidneys.
How Preeclampsia Affects Kidneys
Preeclampsia primarily impacts kidneys through widespread endothelial dysfunction, damage to the inner lining of blood vessels. This systemic damage stems from an imbalance in placental factors, particularly an increase in anti-angiogenic factors like sFlt-1, which interfere with normal blood vessel growth, leading to widespread vascular issues.
The dysfunctional endothelium causes vasoconstriction, significantly reducing blood flow to organs, including the kidneys. While normal pregnancy increases glomerular filtration rate (GFR) by 40-50%, preeclampsia can decrease GFR and renal blood flow by 30-40%.
Reduced blood flow and endothelial damage directly affect the glomeruli, the tiny filtering units. Preeclampsia is associated with glomerular endotheliosis, where endothelial cells swell and block filtering pores, impairing the kidneys’ ability to filter waste.
Disruption of the glomerular filtration barrier leads to protein leakage into the urine. Normally, kidneys retain proteins, but preeclampsia damage allows passage. This protein leakage is a hallmark of kidney involvement and indicates compromised function.
Signs of Kidney Involvement
Proteinuria, excess protein in the urine, is a common indicator of kidney involvement in preeclampsia. While historically a diagnostic requirement, not all individuals show proteinuria. Normal urine protein is typically less than 150 milligrams per day.
In preeclampsia, proteinuria is often defined as 0.3 grams (300 mg) or more in a 24-hour urine sample, or a spot urine protein-to-creatinine ratio of 0.3 or higher. Routine prenatal visits include urine tests to screen for protein; if detected, further quantitative tests like a 24-hour urine collection may confirm the amount lost.
Elevated creatinine levels in the blood are another sign of kidney dysfunction. Creatinine is a waste product filtered by the kidneys; its levels typically decrease during normal pregnancy. Higher-than-normal levels (usually above 0.8 mg/dL) suggest impaired kidney function from preeclampsia.
Reduced urine output (oliguria) signals kidney involvement in severe preeclampsia. This occurs when kidneys produce insufficient urine (often less than 500 cubic centimeters in 24 hours). Oliguria can indicate acute kidney injury, reflecting condition severity.
Blood tests assess kidney function, including serum urea and uric acid levels. These, along with creatinine, provide a comprehensive picture. Monitoring helps evaluate damage and guide treatment.
Protecting Kidney Health
Managing preeclampsia to protect kidney health involves close medical supervision and blood pressure control. Providers monitor blood pressure frequently, as readings of 140/90 mmHg or higher, or severe readings of 160/110 mmHg or higher, are diagnostic criteria. Medications may be prescribed to lower blood pressure and prevent organ damage.
Delivery of the baby and placenta is the definitive treatment for preeclampsia, resolving the underlying cause. Timing depends on preeclampsia severity and gestational age. In severe cases, delivery may be induced even if not full-term, to prevent life-threatening complications.
After delivery, kidney function typically recovers, though healing can take time. Many individuals see kidney markers, such as creatinine and proteinuria, return to normal within weeks or months postpartum. Some may require ongoing monitoring for full recovery.
Individuals with a history of preeclampsia, especially severe or early-onset cases, face an increased long-term risk of chronic kidney disease, hypertension, and cardiovascular disease. Regular follow-up after pregnancy is important to monitor blood pressure and kidney function, helping identify and manage potential long-term complications.