Did you know that pregnancy can affect your kidney-related labs like the serum creatinine test? Creatinine is a waste product of muscle metabolism. Since your kidneys filter creatinine out of your blood, your level of serum (blood) creatinine (SCr) is used to calculate your kidney function, also known as your estimated glomerular filtration rate (eGFR). High serum creatinine indicates kidney disease. During pregnancy, the amount of creatinine in your blood tends to go down. This aberration leads to inaccurate kidney function tests in pregnant women who are also living with chronic kidney disease (CKD). 

In a retrospective study published in Scientific Reports, researchers examined the connections between inaccurate eGFR, actual kidney function, and unfavorable pregnancy outcomes. Learn about what they did, what they found, and what it means for pregnant women with CKD.* 

What they did

Creating a model that can help predict adverse pregnancy outcomes is necessary in order to find ways to prevent them. Using data from Wonju Severance Christian Hospital (WSCH), researchers analyzed the risk of unfavorable pregnancy outcomes in 4,004 pregnant women who were also living with CKD. The adverse outcomes included:

• Preterm birth, 
• Preeclampsia,   
• Fetal growth retardation, and 
• Intrauterine fetal demise. 

The participants were grouped into three categories of kidney dysfunction (mild, moderate, severe) and four categories based on gestational age, or how many weeks a pregnancy has progressed. 

Previous studies established that, as gestational age increases, the mother’s GFR increases and the serum creatinine level decreases. This means that pregnant women with varying levels of actual kidney dysfunction could have normal lab test results.

What they found

By developing a new formula involving blood creatinine adjusted by gestational weeks, the researchers were able to more accurately predict the risk of adverse pregnancy outcomes. 

Elevated SCr levels were significantly associated with that risk, with results showing a steady pattern of adverse pregnancy outcomes increasing as gestational age increased and kidney function decreased.

What it means

The study’s findings show that the new algorithm could be used to identify pregnant women who have reduced kidney function but whose serum creatinine test results are normal.

Awareness of the increased risk would enable doctors to intervene earlier and help prevent adverse pregnancy outcomes.

The researchers also mention that another protein, cystatin C, is more stable than creatinine in the blood during the first and second trimesters of pregnancy, and is elevated during the third trimester. Multiple studies suggest that GFR estimates resulting from a combination of creatinine and cystatin C are more accurate than those resulting from either creatinine or cystatin C alone. 

Because of this, the study authors suggest that the kidney function of pregnant women, especially those at high risk of adverse outcomes, be measured with multiple indicators such as creatinine and cystatin C.

*Kang, J., Hwang, S., Lee, T.S. et al. (2022). Gestational age-specific serum creatinine can predict adverse pregnancy outcomes. Scientific Reports 12, 11224. https://doi.org/10.1038/s41598-022-15450-w