Application of serum sFlt-1/PlGF ratio combined with uterine artery bl

Introduction

Preeclampsia (PE), a multisystem disorder unique to pregnancy, poses a grave global threat to maternal and fetal health. In China, its incidence reaches approximately 9%,¹ with early-onset PE (diagnosed before 34 gestational weeks) representing a critical subset characterized by rapid progression, severe complications, and significant perinatal mortality.² The core pathophysiology involves defective trophoblast invasion and impaired spiral artery remodeling, triggering placental ischemia and systemic endothelial dysfunction through anti-angiogenic and pro-inflammatory cascades.³

Despite decades of research, early prediction remains challenging due to the multifactorial etiology. Current single-modality approaches exhibit limited sensitivity, underscoring the need for integrated biomarker and hemodynamic assessment.⁴ Notably, the soluble fms-like tyrosine kinase-1/placental growth factor (sFlt-1/PlGF) ratio has emerged as a pivotal angiogenic biomarker. sFlt-1 antagonizes PlGF and VEGF, inducing vascular endothelial damage—a hallmark of PE. Prospective studies confirm its utility in predicting early-onset PE 5–8 weeks before clinical manifestation.^5–7 Concurrently, first-trimester uterine artery Doppler ultrasonography provides direct insight into placental perfusion, where elevated pulsatility index (PI), resistance index (RI), or systolic/diastolic (S/D) ratios signify impaired uteroplacental flow, strongly correlating with early-onset PE.^8,9

While both modalities individually demonstrate prognostic value, previous attempts to combine them have yielded inconsistent outcomes. Key limitations include heterogeneous study populations, varying diagnostic thresholds, and lack of standardized timing for biomarker sampling and Doppler assessment.^10,11 Moreover, existing models often fail to address the dynamic interplay between angiogenic imbalance and hemodynamic changes during the first-trimester “window of opportunity” for early intervention.¹² This knowledge gap impedes clinical consensus on optimal combined screening protocols.

To bridge this deficit, our study rigorously evaluates the synergistic efficacy of sFlt-1/PlGF ratio and first-trimester uterine artery Doppler. We hypothesize that their integration will outperform standalone markers, providing a robust tool for timely risk stratification and guiding targeted prevention strategies in high-risk cohorts.

Materials and Methods

Study Population and Grouping

We retrospectively enrolled 148 pregnant women who received prenatal care and delivered at our institution between July 2023 and June 2024. Participants aged 21–35 years (mean 28.58 ± 3.27) were stratified into two groups per the Diagnosis and Treatment Guidelines for Hypertensive Disorders in Pregnancy (2020): Control group: Normotensive pregnancies (n = 76); Early-onset PE group: Preeclampsia diagnosed before 34 weeks (n = 72). This study was approved by the Ethics Committee of the Second Affiliated Hospital of Shandong First Medical University (Approval No. 2022–032-HK). All procedures were conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants.

Inclusion Criteria

① Singleton pregnancy

② Complete clinical/follow-up data.

Exclusion Criteria

① Systemic pathologies (eg, diabetes, chronic hypertension);

② Malignancy;

③ Major fetal anomalies;

④ Medications affecting study parameters.

Research Methods

Biomarker Assessment: At enrollment, demographic and obstetric variables were retrospectively recorded. Venous blood samples (5 mL) were collected from all participants between 24+0 and 27+6 weeks’ gestation. After centrifugation at 3,000 rpm for 10 minutes, the serum was separated and aliquoted into two cryovials for storage. Concentrations of soluble fms-like tyrosine kinase-1 (sFlt-1) and placental growth factor (PlGF) were measured using electrochemiluminescence immunoassays (ECLIA) with commercial kits (Elecsys^® sFlt-1 and PlGF assays; Cat. No. 05168541 190 and 05168743 190, Roche Diagnostics) on a Cobas e 601 analyzer. The sFlt-1/PlGF ratio was automatically calculated by the instrument’s software.

Doppler Ultrasound: Between 24 and 28 weeks of gestation, uterine artery blood flow was assessed using a color Doppler ultrasound system (M22; Wuhan Dongfang Yijing Medical Equipment Co., Ltd.) equipped with a 3–5 MHz convex probe. The following standardized settings were applied: pulse repetition frequency of 1.5–2.5 kHz, wall filter between 50 and 100 Hz, Doppler insonation angle ≤30°, and a sample gate size of 2 mm. Uterine artery pulsatility index (PI), resistance index (RI), and systolic/diastolic velocity ratio (S/D) were measured bilaterally. Three consecutive waveforms were acquired on each side, and the average values for PI, RI, and S/D were recorded for analysis.

Statistical Analysis

Data were analyzed using SPSS 20.0 (IBM Corp). Continuous variables (mean ± SD) were compared via independent t-tests; categorical data (%) via χ²-tests. Logistic regression identified PE predictors. ROC curves evaluated the predictive value of sFlt-1/PlGF, Doppler indices (PI/RI/S/D), and their combination. P < 0.05 indicated statistical significance. Although the cohort size (n = 148) may appear limited, a post-hoc power analysis confirmed >90% power (α=0.05) to detect AUC differences ≥0.15 – a clinically meaningful threshold for predictive models.

Results

Baseline Characteristics

As shown in Table 1, no significant differences existed in maternal age, pre-pregnancy BML, weight gain, or parity distribution between groups (P > 0.05). Gestational age at delivery was significantly lower in the PE group (34.23 +3.04 vs.38.71 +0.81 weeks; t = 11.65, P < 0.001), consistent with early-onset disease.

Table 1 Baseline Characteristics of the Study Cohort

Angiogenic Biomarkers and Doppler Parameters

PlGF levels were significantly lower in the PE group (1.22 ± 0.14 vs 1.54 ± 0.30 μg/L; t = 9.011, P < 0.001). sFlt-1 levels (24.02 + 6.68 vs.16.38 ± 7.47 ug/L; t = 7.654, P < 0.001) and sFlt-1/PIGFratio (20.76 + 7.71 vs.10.11 ± 4.10; t = 12.854, P < 0.001) were markedly elevated (Table 2).

Table 2 Serum Angiogenic Marker Profiles

Uterine artery Doppler indices (PI, RI, S/D) were significantly increased in the PE group (P < 0.001 for all; Table 3). Figure 1 illustrates representative waveforms, showing elevated resistance and diastolic notching in PE cases.

Table 3 Uterine Artery Doppler Parameters

Figure 1 Uterine Artery Doppler at 27+6 Weeks (A) Control: Low-resistance flow (normal) (B) PE: Elevated resistance with diastolic notch.

Multivariate Predictors of Early-Onset PE

Logistic regression identified all six parameters as independent predictors (P < 0.05; Table 4). The sFlt-1/PlGF ratio demonstrated the highest effect size (OR = 1.332, 95% CI: 1.128–1.573), followed by RI (OR = 1.221, 95% CI: 1.087–1.372).

Table 4 Multivariate Analysis of PE Predictors

Predictive Performance of sFlt-1/PlGF Ratio, Uterine Artery Pulsatility Index (PI), and the Combined Model for Early-Onset Preeclampsia

As shown in Table 5, the predictive performance of the combined model incorporating both the sFlt-1/PlGF ratio and uterine artery PI was superior to either parameter alone. The area under the curve (AUC) for the combined model reached 0.954 (95% CI: 0.92–0.99), with a sensitivity of 82.2% and specificity of 96.7%. This model also achieved a positive predictive value (PPV) of 91.9%, negative predictive value (NPV) of 91.7%, and overall accuracy of 94.7%. In comparison, the sFlt-1/PlGF ratio alone yielded an AUC of 0.887 (95% CI: 0.83–0.94), while uterine artery PI alone had a lower AUC of 0.821 (95% CI: 0.75–0.89). These findings suggest that combining biochemical and hemodynamic markers significantly enhances diagnostic performance for early-onset preeclampsia.

Table 5 Predictive Performance of sFlt-1/PlGF Ratio, Uterine Artery Pulsatility Index (PI), and the Combined Model for Early-Onset Preeclampsia

Discussion

This retrospective cohort study systematically evaluated the clinical value of combining serum sFlt-1/PlGF ratio with uterine artery Doppler parameters in predicting early-onset preeclampsia (EOP). The results demonstrated that the PE Group had significantly elevated sFlt-1 levels and decreased PlGF levels, with the sFlt-1/PlGF ratio nearly doubling compared to the control group (20.76 vs 10.11). Moreover, uterine artery Doppler indices (PI, RI, and S/D) exhibited high-resistance flow characteristics. Further multivariate analysis revealed that the sFlt-1/PlGF ratio was the strongest independent predictor of EOP (OR = 1.332), and the combined model (sFlt-1/PlGF + PI) yielded an AUC of 0.954 (95% CI: 0.92–0.99), significantly outperforming individual predictors (sFlt-1/PlGF AUC = 0.887; PI AUC = 0.821).¹³ These findings confirm the synergistic predictive power of molecular biomarkers and hemodynamic parameters in EOP and provide a more accurate tool for clinical risk stratification.

The sFlt-1/PlGF ratio, a core indicator of angiogenic imbalance, plays a pivotal role in the pathophysiology of EOP. sFlt-1, a soluble isoform of vascular endothelial growth factor receptor 1 (VEGFR-1), competitively inhibits VEGF and PlGF, leading to endothelial dysfunction and placental ischemia-hypoxia. In this study, the PE Group showed significantly elevated sFlt-1 levels (24.02 vs 16.38 μg/L) and decreased PlGF levels (1.22 vs 1.54 μg/L), indicating an imbalance between anti-angiogenic and pro-angiogenic factors.¹⁴ This imbalance resulted in a markedly increased sFlt-1/PlGF ratio (20.76 vs 10.11), potentially contributing to EOP through the following mechanisms: First, elevated sFlt-1 inhibits PlGF-mediated trophoblast invasion and spiral artery remodeling, reducing placental perfusion and triggering local hypoxia and oxidative stress; second, hypoxia activates the nuclear factor-κB (NF-κB) pathway, inducing pro-inflammatory cytokines (eg, TNF-α, IL-6), which exacerbate systemic endothelial damage and hypertension; third, the sFlt-1/PlGF imbalance directly injures endothelial cells and promotes vasoconstrictors (eg, endothelin-1), increasing peripheral vascular resistance.^15,16 This mechanistic cascade complements findings from previous studies showing that a sFlt-1/PlGF ratio >38 predicts a 36.7% risk of developing EOP within four weeks,¹⁷ highlighting the ratio’s dynamic association with disease progression.

Simultaneously, the elevated uterine artery Doppler parameters (PI = 1.34 vs 0.82; RI = 0.78 vs 0.51; S/D = 3.89 vs 2.11) reflect the hemodynamic hallmark of inadequate placental perfusion. In normal pregnancy, uterine arteries undergo low-resistance remodeling (PI < 0.8). The high PI in the PE Group suggests inadequate trophoblast-mediated spiral artery remodeling, leading to narrowed lumens and restricted blood flow.¹⁸ This high-resistance state causes intermittent placental hypoxia, oxidative stress, and subsequent endothelial injury, perpetuating a vicious cycle via inflammatory mediators such as sFlt-1. Moreover, increased uterine artery resistance may activate systemic vasoconstriction pathways, further aggravating hypertension.¹⁹ These findings align with prior studies identifying abnormal uterine artery flow as an early warning sign of EOP.²⁰ Notably, the sFlt-1/PlGF ratio and uterine artery PI are complementary: the former captures angiogenic imbalance at the molecular level, while the latter reflects macrovascular hemodynamic alterations. Their combined use spans the entire pathological spectrum from molecular disturbance to blood flow compromise.

On this basis, the combined model (sFlt-1/PlGF + PI) demonstrated substantial clinical advantages. The model’s AUC (0.954) significantly exceeded that of individual indicators (P < 0.001), achieving sensitivity of 82.2%, specificity of 96.7%, and overall accuracy of 94.7%—meeting the criteria for clinical utility.¹³ These results resonate with prior findings that multiparametric models (eg, MAP, PlGF, UTPI, and maternal risk factors) enhance predictive accuracy for EOP.¹⁷ However, the strength of our model lies in its simplicity and potential for dynamic monitoring. It requires only one serum test and one ultrasound scan, making it particularly suitable for resource-limited primary care settings. In addition, longitudinal changes in the sFlt-1/PlGF ratio can reflect ongoing placental function, while the PI remains stable between 24 and 28 weeks of gestation, making it ideal for early prediction. Compared to individual markers, the sFlt-1/PlGF ratio may be influenced by hormonal fluctuations, and PI alone lacks sensitivity for mild cases. By integrating molecular biomarkers with hemodynamic assessments, the combined model overcomes these limitations, offering a scientific basis for EOP stratified management. This integrative approach confirms the synergistic value of biomarkers and Doppler indices and holds promise as a standardized screening strategy for early detection of EOP.²¹

Limitations and Future Directions

Despite the promising findings, this study has some limitations. First, the number of EOP cases (n = 72) was relatively small, which may limit the generalizability of the combined model (sFlt-1/PlGF + PI) across diverse populations. Future validation with larger cohorts is necessary to confirm its stability.¹³ Second, participants were exclusively Chinese Han women, and the applicability of the findings to other ethnicities and regions remains uncertain. Multiethnic or international multicenter studies are needed to assess the model’s broader applicability. Third, only a single time-point measurement was performed at 24–28 weeks of gestation. The lack of longitudinal data on sFlt-1/PlGF and uterine artery PI may overlook key pathophysiological transitions. Future studies should incorporate serial measurements to capture the time-dependent dynamics of these biomarkers.^14,16

To address these limitations, future research should focus on the following areas: (1) Conduct large-scale, multicenter prospective studies involving diverse ethnic and geographic populations to validate the clinical value and universality of the combined model. (2) Utilize cutting-edge technologies such as single-cell sequencing and metabolomics to explore the molecular links between sFlt-1/PlGF imbalance and uterine artery flow abnormalities, thus elucidating the mechanistic basis of placental dysfunction. (3) Based on high-risk stratification using the combined model, design individualized intervention strategies (eg, low-dose aspirin, calcium supplementation) and conduct randomized controlled trials to evaluate their effectiveness in preventing EOP onset. These directions will not only refine our understanding of EOP pathogenesis but also advance obstetric risk management in the era of precision medicine.^15,18,19

Conclusion

By integrating the serum sFlt-1/PlGF ratio with uterine artery Doppler parameters, this study developed a highly accurate predictive model for early-onset preeclampsia. The results reveal a synergistic role of angiogenic imbalance and hemodynamic changes in EOP pathogenesis and provide a scientific basis for clinical stratified management. This combined strategy has the potential to become a standardized tool for early EOP screening and ultimately improve maternal and fetal outcomes.

Disclosure

The authors report no conflicts of interest in this work.

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