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Serum creatinine level varies during pregnancy
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Among pregnant women, serum creatinine concentrations quickly dropped in the first trimester, reached a plateau in the second, and slowly rose in the third trimester toward the pre-pregnancy concentration, according to data recently published in JAMA.
“Creatinine-based equations used to estimate glomerular filtration may misclassify renal function during pregnancy, as they depend on a steady state of creatinine balance. Moreover, a 24-hour collection of urine to measure creatinine clearance is impractical. Accordingly, physicians typically rely on [serum creatinine] level,” Ziv Harel, MD, MSc, FRCPC, of the nephrology division at St. Michael’s Hospital in Toronto, and colleagues wrote.
Researchers added that prior studies attempting to define normal levels were hampered by small sample size and possible sample bias.
Harel and colleagues plotted mean serum creatinine levels weekly in 243,534 pregnant women. There were 361,945 measurements taken during the study.
Researchers found the mean serum creatinine concentration was 1.4176 mg/dL prior to pregnancy, quickly dropped by 4 weeks into the pregnancy to a low of 1.1104 mg/dL between 16 and 32 weeks, then slowly rose to a maximum of 1.5121mg/dL a few weeks after delivery, then a gradual return to mean concentrations prior to the pregnancy by 18 weeks’ after delivery. There was also a difference of approximately 0.3544 mg/dL between the 95th and 50th percentiles during pregnancy and of approximately 0.4725 mg/dL after delivery.
“A 95th-percentile serum creatinine concentration may suggest impaired kidney function and prompt further investigation or specialty referral,” Harel and colleagues wrote. – by Janel Miller
Disclosures : The researchers report no relevant financial disclosures.
Perspective
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Amy E. Judy, MD, MPH
Renal disease and dysfunction have a significant impact on maternal health and pregnancy outcomes. As more women pursue pregnancy at older ages and with more preexisting medical conditions than past generations, underlying renal disease has become a greater concern for women of reproductive age. Harel et al’s research letter provides an important resource for providers assessing and counseling patients prior to conception.
That said, the limitations of this study cannot be ignored. Harel and colleagues looked at a very large dataset from the general population. We do not know why these particular women had creatinine levels checked prior to or during pregnancy, as this is not a routine study performed on all women. As a result, these researchers may have under-estimated what creatinine levels are in a healthy pregnant woman.
Recommendations vary with regard to routine screening for renal disease in the general population. Therefore, it is important for primary care physicians to consider risk factors for renal dysfunction in any women considering pregnancy, and to check serum creatinine levels before their patient becomes pregnant in women with pre-existing medical conditions like high blood pressure, diabetes or autoimmune disorders, since women with these conditions are at higher risk for renal insufficiency than women without these conditions.
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