Preeclampsia (PE) is a serious pregnancy-specific hypertensive disorder and remains one of the major causes of maternal and fetal morbidity and mortality worldwide [1]. The condition typically develops after 20 weeks of gestation and is characterised by hypertension accompanied by proteinuria or evidence of systemic organ dysfunction [2]. PE affects approximately 2–5% of all pregnancies and represents an important contributor to maternal mortality, particularly in low- and middle-income settings [3]. Although maternal deaths are rare in developed countries, recent reports indicate that the incidence of PE has increased and that it continues to contribute to maternal mortality [4, 5].

Although the pathogenesis of PE has not yet been fully elucidated, impaired placental invasion, inadequate remodelling of spiral arteries, placental hypoxia, and subsequent endothelial dysfunction are considered key contributing factors [6]. Failure of trophoblasts to reach adequate differentiation and invasion capacity, especially in early pregnancy, leads to decreased uteroplacental perfusion and underlies the development of PE [7].

In this context, adhesion molecules involved in placental development may play determinant roles in the pathogenesis of PE. Cadherins are calcium-dependent transmembrane glycoproteins that provide intercellular adhesion and play an important role in the regulation of the invasive capacity of trophoblasts [8]. Cadherin-6 (CDH-6), a type 2 cadherin, is prominently expressed in extravillous trophoblasts and plays an active role in the development of the kidney and central nervous system during embryogenesis. Controlled invasion of trophoblasts into the decidua during normal pregnancy is facilitated by the regulated expression of CDH-6 and related molecules [9].

A recent study has reported that serum CDH-6 levels may be associated with PE. In a pilot study conducted by Güvey et al. [10], CDH-6 and cadherin-11 (CDH-11) levels were significantly increased, especially in patients with early-onset and severe PE. These findings suggest that cadherin family molecules may have potential not only in placental development, but also in the diagnosis and prediction of pathological conditions.

On the other hand, the need for early biomarkers to predict PE is critical in clinical practice, as the development of PE can be prevented in high-risk pregnant women with the use of low-dose aspirin [11]. However, the methods currently used in clinical practice are often applied only after the onset of overt symptoms. However, several studies have reported that levels of circulating biomolecules may change weeks or even months before the onset of PE [12, 13]. In this context, early detection of CDH-6 may contribute to assessing the risk of PE.

The aim of this study is to investigate the potential of maternal serum CDH-6 levels measured in the early second trimester of pregnancy (15–20 weeks) to predict the subsequent development of PE. This approach may enable earlier intervention against PE and improve maternal and fetal outcomes.

This study was designed as a prospective observational cohort study and conducted in pregnant women followed at the Gynecology and Obstetrics Clinic of Samsun Training and Research Hospital between January 1, 2024, and December 1, 2024. Ethical approval was obtained prior to the analytical phase of the study (Ethics Committee Approval No. GOKAEK-2024/2/15). Blood samples were collected as part of routine antenatal care (triple screening tests) and stored under appropriate conditions. The study was observational in nature, and no additional procedures or interventions were performed prior to ethical approval. Following ethical approval, the stored samples were analyzed, and patients were followed prospectively until delivery. All participants provided written informed consent, and clinical data were obtained from prospectively recorded hospital records. This study was retrospectively registered at ClinicalTrials.gov (https://clinicaltrials.gov/) (Identifier: NCT07467226).

A total of 150 pregnant women were included in the study. Participants were selected from volunteers who presented for triple screening tests, had confirmed gestational age, and met the eligibility criteria. During the follow-up period, 75 pregnant women who met the diagnostic criteria for PE in the subsequent weeks were assigned to the study group. The control group consisted of 75 pregnant women who were followed during the same time period at the same center and who did not develop any pregnancy complications. No individual matching was performed between the groups; therefore, some demographic differences between groups were anticipated.

Pregnant women aged between 18 and 45 years with a singleton pregnancy and a gestational age of 15 to 20 weeks (confirmed by first-trimester ultrasound), whose serum samples obtained during screening tests were stored under appropriate conditions, and who either developed PE during the follow-up or had a healthy pregnancy were included in the study.

Pregnant women with a history of systemic diseases, such as chronic hypertension, pregestational diabetes, and renal disease; autoimmune diseases, such as systemic lupus erythematosus and antiphospholipid syndrome; multiple pregnancies; fetal structural or chromosomal abnormalities; active smoking or alcohol use; and those with a history of drug abuse or immunosuppressive therapy were excluded.

The 75 pregnant women included in the study group consisted of individuals diagnosed with PE in accordance with international guidelines (blood pressure $\ge$140/90 mmHg and/or proteinuria, or signs of end-organ damage) [14]. The following data were collected for all participants: demographic data (age, gravida, parity, body mass index [BMI]); laboratory findings (hemoglobin, platelet count, serum aspartate aminotransferase [AST] and alanine aminotransferase [ALT] levels); serum CDH-6 level (by enzyme-linked immunosorbent assay [ELISA] method); and blood pressure measurements (systolic and diastolic values). Mode of delivery (vaginal delivery or cesarean section) and perinatal outcomes (presence of preterm delivery, gestational week at birth, neonatal birth weight, Appearance, Pulse, Grimace, Activity, Respiration (APGAR) scores, presence of meconium-stained amniotic fluid [MSAF], and neonatal intensive care unit [NICU] admission), were analysed.

In this study, a total of 150 pregnant women who underwent serum sampling during the second trimester and whose birth outcomes were recorded afterwards were included. PE was developed in 75 participants during the subsequent weeks of pregnancy, whereas the remaining 75 completed pregnancy without complications and constituted the control group. Demographic and clinical data were fully recorded for both groups and were available for statistical analyses.

According to the data summarized in Table 1, pregnant women who developed PE were significantly older than controls, with a higher median age (32 [20–43] vs. 26 [19–39] years; p 0.001). Median gravidity and parity were also significantly higher in the PE group compared with the control group (gravidity: 3 [1–8] vs. 1 [1–3], p 0.001; parity: 2 [0–6] vs. 0 [0–2], p 0.001). Median systolic and diastolic blood pressure values were markedly higher in the PE group than in controls (systolic: 170 [155–200] vs. 110 [85–130] mmHg; diastolic: 135 [110–160] vs. 65 [45–80] mmHg; both p 0.001). In addition, median hemoglobin levels were lower (10.2 [7.7–13.7] vs. 11.3 [7.6–14.4] g/dL; p = 0.002), and median platelet counts were also reduced in the PE group (190 [89–392] vs. 209 [101–497] $\times$ 10⁹/L; p = 0.027). Median BMI values did not differ significantly between the groups (25 [21–39] vs. 25 [21–36] kg/m²; p = 0.249).

Table 2 summarizes maternal serum CDH-6 levels and neonatal outcomes. Median CDH-6 levels were significantly higher in the PE group compared with controls (375.3 [189.8–776.0] vs. 93.1 [50.2–201.7] ng/mL; p 0.001). Within the PE cohort, early-onset cases had markedly higher CDH-6 levels than late-onset cases (523.86 [231.18–776.0] vs. 359.69 [189.82–581.81] ng/mL; p 0.001). Regarding perinatal outcomes, median birth weight was significantly lower in the PE group (2700 [1310–5030] g vs. 3500 [3000–3990] g; p 0.001). Median Apgar scores at the 1 and 5 minutes were similar between groups (1 min: 9 [4–9] vs. 9 [4–9], p = 0.434; 5 mins: 9 [4–10] vs. 9 [5–10], p = 0.717). The rate of meconium-stained amniotic fluid did not differ significantly between the PE and control groups (21.3% vs. 14.7%; p = 0.288). NICU admission was higher in the PE group, although not statistically significant (22.7% vs. 17.3%; p = 0.414).

As a secondary analysis, logistic regression was performed to evaluate the association between serum CDH-6 levels and the timing of disease onset among PE cases Table 3. The relationship between serum CDH-6 levels and early-onset (34 weeks) and late-onset ($\ge$34 weeks) PE was evaluated using multivariate logistic regression analysis, adjusted for age, BMI and parity. The analysis revealed that CDH-6 levels were independently and statistically significantly associated with the timing of the disease onset (adjusted odds ratio [AOR] = 0.99, 95% CI: 0.98–0.99; p 0.001). Since CDH-6 was included in the model as a continuous variable, the OR represents the change in risk for each 1 ng/mL increase in serum CDH-6 level. In contrast, age, BMI, and parity were not statistically significant predictors in the multivariable model. However, these variables were retained in the model because they are recognized clinical factors that may act as potential confounders in PE research. These findings suggest that serum CDH-6 levels may be associated with the timing of PE onset among affected cases. However, the current model does not evaluate the independent association between CDH-6 levels and the occurrence of PE compared with controls.

ROC analysis demonstrated that serum CDH-6 levels showed very high discriminatory performance in distinguishing PE from normotensive pregnant women (control group). The AUC was 0.983 (95% CI: 0.96–1.00). Using the Youden index, an optimal cutoff value of 103.5 was identified, yielding a sensitivity of 98.8% and a specificity of 69.1% (Table 4, Fig. 1).

Fig. 1.

ROC curve for serum CDH-6 levels distinguishing PE from normotensive controls.

When PE cases were evaluated internally, ROC analysis revealed that serum CDH-6 levels had good discriminatory ability for distinguishing early-onset (34 weeks) from late-onset ($\ge$34 weeks) disease, with an AUC of 0.801 (95% CI: 0.70–0.90). Based on the Youden index, a cutoff value of 565.1 was identified, providing 96.0% sensitivity and 50.0% specificity (Table 5, Fig. 2).

Fig. 2.

ROC curve for serum CDH-6 levels differentiating early-onset (34 weeks) and late-onset ($\mathrm{\ge }$34 weeks).

The present study demonstrated that maternal serum CDH-6 levels measured between 15–20 weeks of gestation were significantly higher in pregnancies that subsequently developed PE than in normotensive controls. Moreover, the more pronounced elevation observed in early-onset PE suggests that CDH-6 may be particularly useful for early risk stratification in high-risk pregnancies. In the present study, ROC analysis was used as the primary method to evaluate the predictive performance of CDH-6 for PE, whereas logistic regression analyses were performed as secondary analyses to examine the association of CDH-6 with disease subtypes.

PE is a complex pregnancy complication associated with substantial maternal and fetal morbidity, highlighting the importance of early identification of high-risk pregnancies. Despite extensive research on predictive biomarkers, reliable and widely applicable markers for early diagnosis remain lacking [15, 16, 17].

Recent studies have highlighted the roles of cadherins, a family of cell adhesion molecules, in pregnancy physiology and pathology [18, 19]. These molecules, which mediate intercellular adhesion, play a role in critical mechanisms such as trophoblast invasion and spiral artery remodelling during the placentation process [9]. In this context, members of the cadherin family are thought to contribute to the pathogenesis of PE.

A previous study has reported that CDH-11 levels were increased in preeclamptic placental tissues, which may limit trophoblast invasion by affecting cell-cell adhesion [10]. In the same study, CDH-6 levels were also shown to increase in association with PE, with this elevation becoming significant in the later weeks of pregnancy. Consistent with these findings, CDH-6 levels in our study exhibited a similar pattern of increase. In addition to the established roles of CDH-6 and CDH-11 in trophoblast invasion and placental development, recent evidence has highlighted the potential relevance of CDH-18 in PE. A recent study by Gumusburun et al. [20] demonstrated that maternal serum CDH-18 levels measured in the early second trimester were significantly higher in pregnancies that subsequently developed PE, particularly in early-onset cases. These findings strengthen the hypothesis that multiple members of the cadherin family may contribute to the pathophysiology of PE through mechanisms involving abnormal cellular adhesion, impaired trophoblast remodeling, and endothelial dysfunction.

Another notable finding of our study was that CDH-6 levels were higher in the early-onset PE group compared with late-onset cases. This may be explained by the fact that early-onset PE usually shows a more severe clinical course and is pathophysiologically associated with more pronounced endothelial dysfunction [21]. The literature also suggests a correlation between the levels of biomarkers used to predict PE and the severity of this pregnancy complication [10, 22, 23]. Accordingly, CDH-6 may be helpful in predicting not only the risk of PE, but also its severity and timing.

The literature has also reported that afamin, a glycoprotein associated with oxidative stress, exhibits increased serum levels in inflammatory conditions such as PE [12]. The association between oxidative stress markers such as afamine and PE suggests that CDH-6 may also be elevated in response to similar inflammatory processes. However, CDH-6 levels should be evaluated in correlation with other inflammatory and oxidative stress markers in order to establish this situation definitively.

Periostin is another matrix protein associated with PE. Increased periostin levels suggest a role in extracellular matrix remodelling and vascular permeability [24]. Sasaki et al. [25] reported that periostin levels were significantly higher in women with PE and that this increase may also be associated with fetal growth restriction. Similarly, the lower birth weights, lower Apgar scores, and increased NICU admission rates observed in the PE group in our study indicate a poor perinatal prognosis in these patients. In this context, our findings suggest that CDH-6 levels may be associated with perinatal outcomes beyond the diagnosis of PE. However, further studies with a longer follow-up period are needed to confirm this hypothesis and to determine whether CDH-6 is an independent prognostic biomarker.

The biomarker potential of the cadherin family has been demonstrated previously by Ahmed et al. [26], who reported high discriminatory performance based on ROC analysis. Consistent with these findings, we found that maternal serum CDH-6 levels exhibited strong diagnostic accuracy for predicting PE. CDH-6 distinguished preeclamptic pregnancies from normotensive controls with very high ROC performance, supporting its potential value as an early second-trimester screening biomarker. In addition, subgroup analyses showed that CDH-6 effectively differentiated early-onset from late-onset PE, indicating that higher CDH-6 levels may be associated with more severe disease phenotypes. Altogether, these results suggest that CDH-6 has clinically meaningful predictive value and may contribute to risk stratification during mid-pregnancy.

In this study, we reported that maternal serum CDH-6 levels measured in the early second trimester of pregnancy may serve as a significant biomarker for predicting PE that may develop in the subsequent weeks. In addition, higher CDH-6 levels were detected in early-onset cases, suggesting potential utility for early diagnosis of more severe cases of PE. When evaluated alongside perinatal outcomes, our findings suggest that CDH-6 may have not only predictive, but also prognostic value. Future studies with larger sample sizes and multicenter designs are needed to confirm these results and support clinical implementation.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

CSC and NG conceived and designed the study. SSU and YCU collected the data. ODU and SC performed data analysis and interpretation. NG drafted the manuscript. CSC, SC, SSU, ODU and YCU critically revised the manuscript for important intellectual content. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work.

The study was conducted in accordance with the Helsinki Declaration. The research protocol was approved by the Samsun University Non-Interventional Clinical Research Ethics Committee (Ethics Approval Number: GOKAEK-2024/2/15), and all participants provided signed informed consent forms.

Not applicable.

This research received no external funding.

The authors declare no conflicts of interest.

During the preparation of this work, the authors used ChatGPT (OpenAI) for assistance in improving the English language clarity and scientific expression of the manuscript. After using this tool, the authors carefully reviewed and edited the content and take full responsibility for the final version of the manuscript.