sFlt-1/PlGF and beyond: angiolymphatic-associated signatures and emerging biomarkers in placental pathology

Abstract

The placenta is a highly vascularised organ that depends on tightly regulated angiolymphatic networks to sustain normal fetal growth and maternal adaptation to pregnancy. Disruption of these pathways contributes to major obstetric complications, including preeclampsia, fetal growth restriction, gestational diabetes, and stillbirth. In recent years, advances in molecular pathology and high-throughput technologies have identified a spectrum of angiogenic, lymphangiogenic, and endothelial biomarkers that provide mechanistic insights and hold translational promise. Among these, vascular endothelial growth factors (VEGF-A, VEGF-C, VEGF-D), placental growth factor (PlGF), soluble fms-like tyrosine kinase-1 (sFlt-1), angiopoietins, podoplanin, and lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) have emerged as key regulators. Differential expression of these markers in placental tissue, maternal circulation, and extracellular vesicles has been correlated with disease severity, placental morphology, and adverse neonatal outcomes. Despite growing evidence, clinical application is limited by methodological heterogeneity, gestational age–specific variability, and incomplete understanding of lymphatic involvement in placental physiology. This review synthesises current knowledge on angiolymphatic biomarkers in the placenta, highlighting their role in vascular development, disease pathogenesis, and potential as diagnostic and prognostic tools. Future research integrating molecular assays, imaging modalities, and systems biology approaches is essential to standardise biomarker panels and translate them into clinically meaningful strategies for maternal–fetal medicine.

Introduction

Hypertensive disorders of pregnancy and fetal growth restriction (FGR) remain leading causes of maternal and perinatal morbidity and mortality worldwide (1). Despite advances in antenatal care, current prediction and monitoring strategies often fail to identify women at imminent risk, leading to delayed interventions or unnecessary preterm deliveries. The sFlt-1/PlGF ratio has emerged as a pivotal biomarker for predicting and diagnosing preeclampsia, yet it is not sufficient to capture the full spectrum of placental dysfunction. Angiogenesis is central to villous formation and spiral artery remodelling, while immune tolerance is maintained at the maternal–fetal interface. Traditionally, placental pathology has centred around morphological lesions such as infarcts, villitis, and decidual vasculopathy. However, molecular biomarkers have shifted the paradigm, offering refined mechanistic insights into disease pathogenesis and expanding the scope of diagnostic and prognostic evaluation. There is an urgent need for additional biomarkers that reflect complementary pathophysiological pathways, such as lymphangiogenesis, immune modulation, and vascular integrity, to enable more accurate risk stratification and individualised management.

The concept of angiolymphatic biomarkers introduces a new integrative framework that unifies angiogenesis and lymphatic signalling. Although classical lymphatic vessels are absent from the placenta, accumulating evidence suggests that lymphangiogenic programmes remain transcriptionally and functionally active. Such biomarkers are increasingly relevant for predicting adverse pregnancy outcomes, stratifying maternal–fetal risk, and potentially guiding therapeutic interventions (2). While preeclampsia has been the primary focus, angiogenic and lymphatic biomarkers are implicated in a broader spectrum of conditions including FGR, preterm birth, chorioamnionitis, and stillbirth (3). Recent research has expanded beyond classical angiogenic factors to include endothelial glycoproteins, vascular guidance molecules, and lymphatic markers, creating a more nuanced picture of placental vascular biology. This review synthesises emerging evidence on angiolymphatic biomarkers, contextualises their diagnostic and prognostic significance, and identifies critical areas for future research.

Placental angiogenesis: established pathways and clinical implications

The placenta represents a unique vascular organ supporting dual circulation systems – maternal and fetal – that must maintain functional separation while enabling efficient exchange. Recent studies emphasise that placental vascular development follows a tightly regulated spatiotemporal programme, with critical windows occurring at 6–8 weeks (primary villus formation), 12–16 weeks (secondary branching), and 20–24 weeks (terminal villus maturation) (4).

Angiogenesis in the placenta is predominantly driven by vascular endothelial growth factor A (VEGF-A), placental growth factor (PlGF), and their receptors (VEGFR-1, VEGFR-2).These pathways regulate villous vascular branching and uteroplacental perfusion (5). Figure 1 depicts a schematic representation of placental villus structure with the location of various angiogenic markers. VEGF family members orchestrate endothelial proliferation and vascular branching. Among them, VEGF-A is the primary mitogen, while PlGF modulates VEGF signalling, enhancing angiogenesis under hypoxic conditions (6, 7). Additional angiogenic modulators include angiopoietins (Ang-1, Ang-2), endoglin, hypoxia-inducible factors (HIF-1α), endothelial nitric oxide synthase (eNOS), and transforming growth factor-β (TGF-β) all of which integrate environmental cues with vascular remodelling (8, 9).The most clinically validated biomarkers are soluble fms-like tyrosine kinase-1 (sFlt-1) and PlGF. sFlt-1, a soluble VEGF receptor, acts as a decoy, binding VEGF and PlGF, thereby inhibiting angiogenesis (10). Elevated sFlt-1 and reduced PlGF levels characterise preeclampsia and FGR, forming the basis for the sFlt-1/PlGF ratio, which is now incorporated into clinical prediction algorithms in Europe and Asia (10, 11, 12).

Figure 1.

Schematic representation of placental villus structure and angiogenic/lymphangiogenic markers. The image shows a placental villus with syncytiotrophoblast (STB), cytotrophoblast (CTB), villous stroma (VS), fetal blood vessels (BV) with endothelium (E), and Hofbauer cells (HC).Angiogenic factors (VEGF-A, PlGF, Ang-1/Ang-2, eNOS), anti-angiogenic factors (sFlt-1, sEng), and lymphangiogenic markers (VEGF-C/D, VEGFR-3, PROX1, LYVE-1) are indicated.

Beyond this axis, several angiogenic biomarkers have been studied. Soluble endoglin (sEng), a TGF-β co-receptor shed into the maternal circulation, leads to endothelial dysfunction and contributes to disease severity in preeclampsia. Similarly, deregulation of the angiopoietin-Tie2 signalling pathway, specifically increased Ang-2 and decreased Ang-1, is associated with placental insufficiency and poor pregnancy outcomes (8, 13, 14).

Lymphatic signalling in the placenta: a hidden network

Unlike most organs, the human placenta lacks classical lymphatic vessels, as demonstrated by several studies (15, 16, 17). Despite the absence of morphological lymphatic vessels, lymphatic programme markers are paradoxically expressed (Fig. 1). Hofbauer cells express LYVE-1, PROX1, and podoplanin, supporting roles in antigen clearance, hyaluronan turnover, and immune tolerance (18, 19). Syncytiotrophoblasts also express podoplanin, which may substitute for CD44 in hyaluronan regulation (18). Dysregulation of these lymphatic pathways has been linked to pathogenesis in preeclampsia in animal models (20). Hence, the application of lymphatic markers as clinical biomarkers remains at an experimental stage.

Emerging evidence suggests that angiogenic and lymphatic pathways are not independent but interconnected. VEGF-C and VEGF-D can activate both VEGFR-2 (angiogenesis) and VEGFR-3 (lymphangiogenesis), creating a shared signalling interface (21). Hypoxia, a hallmark of abnormal placental development, upregulates VEGF family members, thereby influencing both vascular branching and lymphatic-like programmes (22). Cross-regulation also occurs through HIF-1α, which stimulates sFlt-1 expression, indirectly shifting the balance toward anti-angiogenesis while altering stromal immune functions. A striking in vivo example of cross-programming is ‘lymphatic mimicry’ during spiral artery remodelling (23). Using genetic mouse models and in vitro assays, Pawlak et al. demonstrated that maternal endothelial cells in remodelled spiral arteries transiently express PROX1, LYVE-1, and VEGFR-3, a phenotype driven in part by uterine NK-cell–derived VEGF-C, and this facilitates lumen enlargement to achieve the high-flow, low-resistance state required for placentation (23). They further suggested that this ‘lymphatic mimicry’ during spiral artery remodelling may be protective against preeclampsia (23).

sFlt-1/PlGF: the canonical biomarker in placental pathology

Angiogenesis in the placenta is tightly regulated by a balance of pro- and anti-angiogenic factors. sFlt-1, a truncated variant of VEGFR-1, binds and sequesters PlGF and VEGF, suppressing their angiogenic effects (24). In normal pregnancy, PlGF rises in early gestation to support vascular branching and then is balanced by sFlt-1 in later stages to prepare for delivery. In preeclampsia, placental hypoxia induces HIF-1α, which stimulates increased sFlt-1 and VEGF gene expression, but PlGF levels are paradoxically suppressed, resulting in a steep imbalance (24). Elevated maternal serum sFlt-1, particularly in relation to PlGF, correlates with endothelial dysfunction, hypertension, and adverse pregnancy outcomes (10, 25). These alterations mirror impaired angiogenesis and endothelial dysfunction in preeclampsia and FGR (10, 26). Tissue-based studies reveal reduced capillary density, altered Tie2/Ang-2 ratios, and aberrant Notch signalling, which may serve as histopathological adjuncts to serum biomarkers in preeclampsia (27, 28).

The sFlt-1/PlGF ratio is a well-established biomarker recommended by multiple international guidelines for the diagnosis and prediction of preeclampsia (29, 30). Clinically, the maternal serum sFlt-1/PlGF ratio is elevated weeks before symptoms appear and serves as a robust predictor of preeclampsia, particularly early-onset disease (31). A threshold ratio above ≥85 has been suggested both diagnostically and prognostically, while a cut-off ≤38 between 24–37 weeks holds high negative predictive value (up to 99.9%) for ruling out imminent disease (32). Serial monitoring assists in guiding delivery timing, and normalisation indicates treatment response. Key trials such as PROGNOSIS have validated its clinical utility, PARROT-2 demonstrated cost-effectiveness, and PETRA evaluated biomarker-guided interventions (33, 34, 35, 36). These findings have supported the development of assays now FDA-approved with diagnostic accuracy around 94% for severe preeclampsia within 2 weeks of risk assessment. Commercial platforms such as the Elecsys sFlt-1/PIGF ratio assay (FDA-approved), DELFIA Xpress, and Triage PIGF allow rapid, reliable clinical testing (37, 38). The COMPARE study demonstrated that the PlGF-based tests (DELFIA Xpress, Triage PlGF, and Elecsys sFlt-1/PlGF ratio) perform similarly in predicting the need for delivery within 14 days of testing in women with suspected preterm pre-eclampsia (37).

Besides its primary role in the prediction, diagnosis, and management of preeclampsia, the sFlt-1/PIGF ratio and PIGF levels have several other clinical applications related to placental dysfunction. These include differentiating placental versus non-placental causes of FGR, where low PlGF and high sFlt-1 indicate true placental insufficiency and correlate with adverse outcomes (26, 39, 40). The ratio is also useful in distinguishing gestational hypertension from preeclampsia, especially in atypical cases, and in identifying superimposed preeclampsia in chronic hypertension (41). In addition, it helps in assessing the severity of HELLP syndrome and placental abruption, conditions associated with profound angiogenic imbalance (12). Extremely low PlGF levels have been linked to an increased risk of stillbirth and intrauterine fetal demise, while some studies suggest an association with spontaneous preterm birth secondary to placental dysfunction. In a Cochrane systematic review of 21 studies involving 100,687 pregnancies, Heazell et al. identified PlGF as the most accurate biochemical predictor of stillbirth, with a diagnostic odds ratio of 49.2 (95% CI: 12.7–191) (42). Rana et al. reported that an sFlt-1/PlGF ratio ≥85 predicted adverse pregnancy outcomes, including preterm birth, with 94% specificity before 34 weeks of gestation (43). In twin pregnancies, the ratio aids in differentiating pathological preeclampsia from physiological blood pressure changes and is under investigation for predicting selective FGR and complications such as twin-to-twin transfusion syndrome (44, 45, 46).

Emerging angiolymphatic biomarkers beyond sFlt-1/PlGF

Following sFlt-1/PIGF, sEng, an anti-angiogenic glycoprotein, is recognised as a key biomarker of placental pathology, especially in preeclampsia (47, 48, 49). Elevated maternal serum sEng reflects abnormal placental development and is linked to hypertension, FGR, and maternal vascular malperfusion (50, 51). Pathophysiologically, high sEng disrupts TGF-β signalling, impairing trophoblast invasion and spiral artery remodelling, which leads to placental ischaemia and systemic vascular dysfunction. Clinically, elevated sEng in early pregnancy can predict preeclampsia before symptoms appear, while its levels correlate with disease severity and adverse outcomes (47, 52). sEng complements markers such as sFlt-1 and PIGF in risk stratification and is strongly associated with maternal vascular malperfusion lesions (50, 52). Emerging evidence also links it to retained placenta and postpartum haemorrhage (53). Although most effective when combined with other biomarkers and clinical parameters, sEng holds promise for improving early detection and management of placental disease.

Angiopoietins, particularly Ang-1 and Ang-2, are key regulators of placental vascular development. Ang-1 promotes vessel stability and trophoblast growth via Tie-2 signalling, whereas Ang-2 counteracts Ang-1 to maintain vascular plasticity. An imbalance – low Ang-1 and high Ang-2 – is associated with preeclampsia, FGR, and malaria-related placental pathology due to impaired perfusion and vascular instability (13). Bayor et al. found that maternal serum Ang‐2 levels, but not Ang‐1, were markedly reduced in women with preeclampsia compared to normotensive pregnant controls (14). Their expression levels in placental tissue correlate with disease severity in preeclampsia, highlighting their potential as tissue biomarkers (8, 27). The netrin family, initially recognised as axon guidance molecules, also plays an essential role in vascular development and placental angiogenesis (54). Netrin-1 supports endothelial cell survival and migration, while netrin-4 contributes to vascular basement membrane organisation. In the placenta, netrin-1 expression is upregulated under hypoxic conditions, suggesting a compensatory mechanism. Clinically, elevated maternal serum levels of netrin-1 have been associated with early-onset preeclampsia (55).

In a recent case–control study by Bai et al., first-trimester maternal serum analysis identified three angiogenic biomarkers, soluble neuropilin 1 (sNRP-1), soluble platelet and endothelial cell adhesion molecule 1 (sPECAM-1), and platelet-derived growth factor AB/BB (PDGF-AB/BB) as novel predictors of early-onset FGR, with their combination outperforming pregnancy-associated plasma protein-A (PAPP-A), a conventional first-trimester screening marker of placental function and fetal growth (3). sNRP-1 is a cleaved, soluble form of NRP-1, a transmembrane receptor essential for sprouting angiogenesis via tip cell function (56, 57). NRP-1 serves as a co-receptor for VEGFA, enhancing VEGFR-2 signalling to drive endothelial proliferation and migration (56). In contrast, sNRP-1 antagonises NRP-1, acting as an anti-angiogenic factor by blocking VEGF binding and downstream signalling. NRP-1 is normally expressed in decidua and trophoblast throughout pregnancy, supporting implantation and placentation, but is downregulated in FGR placentas (57). While one recent study reported reduced maternal plasma sNRP-1 in FGR with abnormal Doppler findings, Bai et al. showed elevated levels at 11–13 weeks (3, 57). Elevated early sNRP-1 may reflect impaired branching angiogenesis underlying early-onset FGR. sPECAM-1, the soluble antagonist of PECAM-1, interferes with angiogenesis by disrupting endothelial signalling, migration, proliferation, and cell–cell junction formation. In the placenta, PECAM-1 is normally expressed on villous and decidual endothelium. Earlier studies reported no change in placental PECAM-1 in FGR, and findings in preeclampsia were either unchanged or reduced (58). Serum PECAM-1 levels have also shown no significant differences in preeclampsia (59). Bai et al. examined maternal circulating PECAM-1 in FGR and demonstrated elevated levels in the first trimester (3).

Several studies highlight the diverse roles of podoplanin in placental biology. Bellini et al. observed podoplanin-positive stromal cells in chorionic villi, suggesting they act as primitive lymphatic channels, while Wang et al. linked podoplanin to fetal angiogenesis and implicated its reduction in gestational disorders (15, 18). Lee et al. described a podoplanin-positive primovascular system in villi and umbilical cord with immunomodulatory and regenerative functions (60). In Kandemir et al. study of 198 placentas (control, molar, inflammatory, and hypoxic–ischaemic groups), podoplanin expression was graded immunohistochemically. Increased podoplanin expression was noted with placental maturation, while its expression was reduced in molar pregnancies, unchanged in acute inflammation, and markedly elevated in preeclampsia (61).

Table 1 (3, 10, 11, 16, 17, 25, 26, 27, 28, 47, 48, 49, 50, 51, 57, 58, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71) enumerates the key angiolymphatic-related biomarkers in placental pathology, while Table 2 (10, 11, 21, 25, 26, 61, 63, 72, 73, 74, 75, 76, 77) summarises the relative changes in angiogenic and lymphangiogenic markers in major pregnancy complications. Most of these biomarkers related to placental lymphangiogenesis remain at the research stage and are not yet validated for routine clinical use. Comparative studies of biomarker combinations indicate that multimarker approaches – integrating angiogenic imbalance markers (sFlt-1/PlGF), maternal risk factors, and uterine artery Doppler indices – perform better than any single biomarker alone (58). This highlights the value of a precision-medicine strategy, where biomarker panels can be selected based on gestational age, clinical context, and available resources.

Table 1.

Key angiolymphatic-related biomarkers in placental pathology (3, 10, 11, 16, 17, 25, 26, 27, 28, 47, 48, 49, 50, 51, 57, 58, 59, 63, 64, 65, 66, 67, 68, 69, 70, 71).

Biomarker class	Representative markers	Biological role	Detection method	Relevance to placental pathology	References
Angiogenic pathways	VEGF-A, VEGFR-2, PlGF, VEGFR-1 (Flt-1)	Endothelial proliferation, maternal–fetal vascular regulation	ELISA (on maternal blood), IHC, qPCR	Elevated sFlt-1/PlGF ratio is used clinically in preeclampsia; deregulated VEGF signalling in FGR and preeclampsia	(10, 11, 21, 25, 26, 63)
	Ang-1, Ang-2, Tie2	Vessel stabilisation vs remodelling	IHC, multiplex assays (on placental tissue)	Imbalance associated with abnormal vascular maturation, preeclampsia	(27, 28)
	HIF-1α	Hypoxia sensing, angiogenic induction	IHC, WB, qPCR (on placental tissue)	Increased expression in hypoxic villi; marker of FGR and preeclampsia	(63, 64)
	Notch/DLL4, EphrinB2/EPHB4	Arterial–venous specification	IHC, in situ hybridisation	Altered signalling linked to defective branching angiogenesis	(65)
	sEng (soluble endoglin)	Anti-angiogenic, TGF-β pathway inhibition	ELISA (circulating proteins)	Elevated in severe preeclampsia, HELLP syndrome	(47, 48, 49, 50, 51)
	sNRP-1, sPECAM-1, PDGF-AB/BB	Promotes and regulated angiogenesis	ELISA (on maternal blood)	Predictive biomarker of early-onset FGR	(3, 57, 58)
Endothelial identity markers	CD31, vWF, VE-cadherin	Pan-endothelial markers	IHC (on placental tissue)	Identify placental vessel density, distribution, and pathology	(16, 17, 66)
Lymphatic-associated markers	PROX1	Master transcription factor for lymphatic fate	IHC, IF, qPCR (on placental tissue)	Rarely expressed; reported in stromal subsets, suggests lymphatic-like programming	(17)
	LYVE-1	Hyaluronan receptor in lymphatic vessels	IHC, IF (on placental tissue)	May mark macrophages with vascular/immune roles; misinterpreted as lymphatic vessels	(17)
	Podoplanin (D2-40)	Lymphatic endothelial marker	IHC (on placental tissue)	Detected in trophoblast or stromal cells; suggests lymphatic mimicry	(16, 17)
	VEGF-C, VEGF-D, VEGFR-3 (Flt-4)	Lymphangiogenesis drivers	IHC, ELISA, qPCR (on placental tissue)	Dysregulated signalling may influence villous vascular remodelling	(67)
Nucleic acids & extracellular vesicles	miR-210, miR-126, miR-221/222	Angiogenesis-related microRNAs	qPCR, RNA-seq (on maternal blood)	Dysregulation linked to preeclampsia, FGR	(68, 69, 70)
Imaging-based biomarkers	Vessel density, branching patterns, vascular indices	-	Digital pathology, multiphoton imaging, Doppler US	Quantitative assessment of vascular remodelling in placental pathology	(70, 71)

VEGF, vascular endothelial growth factor; VEGFR, vascular endothelial growth factor receptor; PlGF, placental growth factor; sFlt-1, soluble Fms-like tyrosine kinase-1; Ang, angiopoietin; LYVE-1, lymphatic vessel endothelial hyaluronan receptor 1; PROX-1, prospero homoeobox 1; FGR, fetal growth restriction; HELLP, haemolysis, elevated liver enzymes, and low platelets.

Table 2.

Placental angiolymphatic markers and their alterations in pregnancy complications with approximate fold changes (10, 11, 21, 25, 26, 61, 63, 72, 73, 74, 75, 76, 77).

Marker	Preeclampsia	FGR	GDM	References
VEGF-A/VEGF-C/VEGF-D	↓ ∼40–50%	↓ ∼40–50%	Altered (variable)	(10, 11, 21, 72)
PlGF	↓ >70% (serum <30 pg/mL)	↓ ∼50–60%	Altered	(10, 21, 25, 26, 63, 73)
sFlt-1	↑ 3–5× (serum >4,000–5,000 pg/mL)	↑ (∼2–3×)	↑ (∼1.5–2×)	(10, 21, 25, 26, 63, 73)
Ang-1/Ang-2	Ang-2 ↑ (1.5–2×), Ang-1 ↓ (∼30%)	Ang-2 ↑ (∼1.5×)	Altered	(74, 75)
Podoplanin/LYVE-1/PROX-1	Altered	Altered	Altered	(61, 76, 77)

VEGF, vascular endothelial growth factor; PlGF, placental growth factor; sFlt-1, soluble Fms-like tyrosine kinase-1; Ang, angiopoietin; LYVE-1, lymphatic vessel endothelial hyaluronan receptor 1; PROX-1, prospero homoeobox 1; FGR, fetal growth restriction; GDM, gestational diabetes mellitus.

Technical considerations

Biomarkers in placental research have historically been divided into two broad categories: structural features observed in tissue sections or tissue-based biomarkers and soluble proteins measurable in maternal circulation. Accurate interpretation of angiolymphatic biomarkers relies heavily on methodological standardisation and pre-analytical control. For tissue-based biomarkers, sampling should encompass both central and peripheral placental regions, since vascular density and villous architecture vary spatially (78). For circulatory biomarkers in maternal blood, both biological and pre-analytical variables significantly affect reliability. Both sFlt-1 and PlGF exhibit dynamic trajectories during pregnancy, with PlGF peaking around mid-gestation and sFlt-1 rising steeply in the third trimester (79). Consequently, the diagnostic performance of a single threshold may differ substantially between early-onset and late-onset disease, necessitating gestational age–specific reference ranges and interpretation frameworks (12, 32, 79). Circadian rhythms influence analytes such as VEGF and PlGF, which peak in the morning, highlighting the need for standardised collection times (80). Storage conditions are equally important – multiple freeze–thaw cycles can reduce biomarker concentrations by 10–15% (81). Such key technical and pre-analytical considerations have been summarised in Table 3 (8, 11, 12, 19, 32, 78, 79, 80, 81). Together, these methodological and pre-analytical considerations emphasise the need for harmonised protocols and stringent quality control when studying placental angiolymphatic biomarkers, both in tissue and in circulation.

Table 3.

Technical considerations in placental angiolymphatic biomarker studies (8, 11, 12, 19, 32, 78, 79, 80, 81).

Stage of workflow	Key considerations	Rationale
For tissue-based biomarkers
Tissue sampling	- Both central and peripheral placental regions should be sampled	Vascular density and villous architecture vary spatially and inconsistent sampling may introduces bias
Tissue fixation	- Minimisation of cold ischaemia along with adequate fixation with 10% neutral buffered formalin	Delayed fixation causes antigen degradation, reducing immunoreactivity of vascular and lymphatic markers, thereby yielding false results
Immunohistochemistry	- Possible antibody cross-reactivity should be taken into account during interpretation – for instance, LYVE-1 may also stain macrophages	It ensures accurate identification of true lymphatic structures and prevent misinterpretation due to marker cross-reactivity
	- To improve specificity, co-localisation studies with pan-endothelial markers (CD31, endomucin) and macrophage markers (CD68, CD163) are recommended
Quantification strategy	- Digital image analysis or morphometric measurements are preferable to subjective scoring	It improves reproducibility and enable statistical comparability, especially in research settings
	- Using continuous metrics (e.g., vessel density, marker area fraction) is preferable
For serum-based biomarkers
Sample collection	- Account for biological variables such as gestational age and circadian rhythm	sFlt-1 and PlGF levels vary with gestational age and diurnal cycles; inconsistent sampling alters diagnostic thresholds
	- Standardise collection timing (preferably morning)
Pre-analytical handling	- Avoid multiple freeze–thaw cycles; store samples under consistent conditions	Minimises degradation and assay interference; maintains biomarker stability
	- Prevent haemolysis and lipaemia; note maternal anaemia if present
Analytical validation	- Cross-validation across different ELISA or multiplex platforms	Addresses inter-assay variability and ensures comparability across laboratories
	- Usage of internal reference standards where available

Recent advancements and future perspectives

Recent advancements in angiolymphatic placental biomarkers reflect a transition from single-marker assessment toward multidimensional vascular and lymphatic characterisation, including the exploration of complementary markers that capture endothelial health and microvascular integrity. Endothelial glycocalyx injury markers such as syndecan-1 have been associated with the severity of preeclampsia and placental dysfunction, while sphingosine-1-phosphate is being studied for its role in maintaining vascular barrier stability and placental perfusion (82, 83). In parallel, extracellular vesicles have emerged as dynamic, non-invasive readouts; profiling vesicle-associated angiogenic proteins such as PlGF and sFlt-1, as well as microRNAs including members of the C19MC cluster, offers promise for early detection and longitudinal monitoring (41, 84). Furthermore, nucleic acid biomarkers – notably microRNAs (miRNAs) regulating angiogenesis and lymphangiogenesis – along with extracellular vesicle cargo released into maternal circulation, represent non-invasive windows into placental angiolymphatic biology (70, 85).

The lymphatic dimension of placentation, although incompletely understood, is receiving renewed attention, with evidence of lymphangiogenic marker expression in the placental bed suggesting maternal vascular and immune adaptations in specific pathological states such as late-onset preeclampsia (86). Looking ahead, future research is leveraging advanced technologies to decode these complex vascular programmes. Multiplexed tissue imaging, including multiplex immunohistochemistry and imaging mass cytometry, enables co-localisation of vascular markers with lymphatic and immune markers to clarify lymphatic-like signalling (87). Three-dimensional vascular quantification using tissue clearing combined with light-sheet microscopy or micro-CT allows precise computation of villous capillary density, branching complexity, and flow surrogates (88).

Artificial intelligence-assisted digital pathology is being adopted to generate continuous quantitative angiometric data, such as capillary length density and lymphatic marker distribution, improving reproducibility over traditional scoring (89). Functional interrogation of vascular signalling is also advancing through organ-on-chip placental models, which enable controlled perturbation of VEGF-C/D–VEGFR-3 and angiopoietin–tie pathways under defined oxygen conditions (90). These experimental innovations complement clinical biomarker development, laying the groundwork for multi-marker panels that integrate angiogenic factors, glycocalyx injury indicators, extracellular vesicle signatures, and spatial vascular metrics. Standardisation of analytical pipelines, establishment of gestation- and phenotype-specific reference ranges, and deployment of microfluidic point-of-care platforms will be critical for translating these biomarkers into real-time tools for individualised obstetric care.

Conclusion

Angiolymphatic biomarkers represent a promising frontier in placental pathology, expanding our understanding from static histomorphology to dynamic molecular and vascular signalling. By bridging angiogenic and lymphangiogenic pathways, they highlight the intricate cross-talk between vascular, stromal, and immune compartments at the maternal–fetal interface. While the well-established sFlt-1/PlGF ratio continues to serve as a cornerstone in the diagnosis and management of preeclampsia and FGR, emerging biomarkers such as soluble endoglin, angiopoietins, podoplanin, neuropilins, and netrins offer new windows into the vascular and lymphatic biology of the placenta. Integration of these markers into standardised, multi-parameter panels, coupled with advanced analytic platforms, holds promise for earlier detection and improved risk stratification.

Declaration of interest

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the work reported.

Funding

This work did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.

Author contribution statement

All the authors have contributed substantially to the conception/design of the work; the acquisition, analysis, and interpretation of data for the work; drafting the work or revising it critically for important intellectual content; final approval of the version to be published; and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. MM, SP were responsible for concept and study design, definition of intellectual content, literature search, manuscript preparation, manuscript review, and finalisation. RM helped in defining the intellectual content, literature search, manuscript preparation, and manuscript review.