Interleukin-6, Proteinuria, and Arterial Stiffness in Preeclampsia: Distinct Inflammatory, Renal, and Vascular Associations

Background: Preeclampsia is characterized by systemic inflammation, endothelial dysfunction, and progressive abnormalities in the maternal vasculature. Interleukin-6 (IL-6) may indicate inflammatory activity, while aortic pulse wave velocity (PWVao) and augmentation index (AIx) offer complementary assessments of arterial stiffness and vascular function. This study examined the relationships among IL-6, proteinuria, and arterial stiffness in women with preeclampsia. Methods: This observational study involved 87 pregnant women with preeclampsia who were evaluated at the Emergency Clinical Hospital “Pius Brînzeu” in Timișoara, Romania. Arterial stiffness was measured non-invasively with the Arteriograph system during the second trimester (20–24 weeks) and the third trimester (32–36 weeks). PWVao served as the primary marker of arterial stiffness, whereas AIx provided a complementary measure of arterial wave reflection. Serum IL-6 levels were quantified by enzyme-linked immunosorbent assay, and 24 h proteinuria was recorded. Associations among inflammatory, renal, and vascular parameters were examined using Spearman correlation analyses. Multivariable linear regression then identified independent predictors of third-trimester PWVao. Results: The mothers had a mean age of 37.59 ± 2.65 years, and the mean BMI was 30.41 ± 2.70 kg/m2. PWVao rose significantly between the second and third trimesters, from 10.94 ± 1.36 m/s to 12.46 ± 1.70 m/s (p < 0.001). AIx also increased, from 1.26 ± 0.85% to 3.66 ± 1.32% (p < 0.001). The mean serum IL-6 concentration was 31.01 ± 35.61 pg/mL. No significant correlation was found between IL-6 and PWVao in either the second trimester (ρ = −0.100, p = 0.356) or the third trimester (ρ = −0.100, p = 0.358), and IL-6 was not significantly correlated with AIx. A significant positive correlation was observed between IL-6 and 24 h proteinuria (ρ = 0.337, p = 0.0014). Proteinuria itself showed no significant association with PWVao or AIx. In the multivariable analysis, only BMI independently predicted third-trimester PWVao (β = 0.634, 95% CI: 0.469–0.799, p < 0.001). Age, systolic blood pressure, proteinuria, and IL-6 showed no independent association with PWVao. Nor were IL-6, proteinuria, or third-trimester PWVao significantly associated with birth weight or the 1 min Apgar score. Conclusions: Among women with preeclampsia, arterial stiffness increased progressively throughout pregnancy. Systemic inflammation, measured by IL-6, was more strongly associated with renal involvement than with mechanical arterial stiffness. BMI was the main independent determinant of third-trimester PWVao. Together, these results support a multidimensional view of preeclampsia, in which inflammatory, renal, metabolic, and vascular abnormalities form related yet partly distinct pathways. Assessing IL-6, proteinuria, BMI, and arterial stiffness together may improve maternal cardiovascular phenotyping and help establish future risk-stratification strategies.