Preeclampsia biomarker screening — скринінг біомаркерів для ранньої прогностики прееклампсії. Angiogenic imbalance between anti-angiogenic sFlt-1 and pro-angiogenic PlGF, combined into a diagnostic ratio.
Healthy placentation depends on coordinated angiogenesis: pro-angiogenic signals (VEGF, PlGF) promote endothelial proliferation and vascular remodeling of the uteroplacental circulation, while counter-regulatory anti-angiogenic factors keep this process in check. In preeclampsia, placental tissue subjected to relative hypoxia and impaired trophoblast invasion releases excess anti-angiogenic factors into the maternal circulation, tipping the balance and producing systemic endothelial dysfunction — the mechanistic thread linking placental pathology to the maternal syndrome of hypertension and proteinuria.
Normal early pregnancy: extravillous trophoblast cells invade the maternal spiral arteries, remodeling them into low-resistance, high-capacitance vessels able to deliver a large blood volume to the developing placenta. This remodeling is angiogenesis-dependent, orchestrated by a network of growth factors acting on maternal and placental endothelium.
In preeclampsia, trophoblast invasion is shallow and spiral artery remodeling is incomplete. The placenta experiences intermittent hypoxia and oxidative/mechanical stress, which in turn triggers release of factors into the maternal bloodstream that interfere with normal angiogenic signaling — most notably an anti-angiogenic protein (sFlt-1) that neutralizes the pro-angiogenic signals (VEGF, PlGF) the maternal vasculature needs to stay healthy.
Why a systemic vascular disease originates in the placenta: • The placenta acts as an endocrine organ, secreting factors directly into maternal circulation • Anti-angiogenic factors circulate systemically, not just locally — explaining why preeclampsia affects kidney, liver, brain, and placental vasculature simultaneously • The imbalance typically becomes biochemically measurable weeks before clinical signs (hypertension, proteinuria) appear, which is the rationale for biomarker-based screening rather than waiting for clinical criteria alone
This two-factor framework — one anti-angiogenic marker rising, one pro-angiogenic marker falling — is the conceptual foundation for the sFlt-1/PlGF screening approach explored in the remaining stages.
The angiogenic imbalance model reframes preeclampsia less as an unpredictable event and more as a biochemically detectable process. Because the imbalance can be measured directly in maternal blood, it offers an opportunity for objective, quantitative screening layered on top of traditional clinical assessment (blood pressure, urine protein, symptoms).
Soluble fms-like tyrosine kinase-1 (sFlt-1) is a truncated, secreted form of the VEGF receptor Flt-1 that lacks a transmembrane domain and instead circulates freely in maternal blood. Functionally it acts as a molecular sponge — binding circulating VEGF and PlGF and preventing them from engaging their normal receptors on maternal endothelial cells. In placental dysfunction, placental villous tissue markedly upregulates sFlt-1 production, and its rising concentration is one of the most consistent biochemical signals observed ahead of, and during, the clinical preeclampsia syndrome.
Mechanism of action: • Full-length Flt-1 (VEGFR-1) is a membrane receptor tyrosine kinase that, when bound by VEGF or PlGF, promotes endothelial survival, vasodilation (via nitric oxide and prostacyclin pathways), and vascular permeability regulation • sFlt-1 is an alternatively spliced, secreted variant retaining the extracellular ligand-binding domain but not the intracellular signaling domain • By binding VEGF and PlGF with high affinity but transmitting no downstream signal, sFlt-1 effectively withdraws these growth factors from circulation — a "ligand trap"
Downstream consequences of elevated sFlt-1: • Maternal endothelial cells are deprived of VEGF/PlGF signaling → reduced nitric oxide production → vasoconstriction and elevated blood pressure • Glomerular endothelial injury (endotheliosis) → proteinuria, the classic renal manifestation • Effects are systemic because sFlt-1 circulates freely, rather than acting only at the placental interface
Clinical trajectory: • sFlt-1 concentrations tend to rise progressively over the weeks preceding overt clinical preeclampsia, often before hypertension or proteinuria become apparent • The magnitude and rate of rise both carry prognostic information, though this simulation treats the level as a single illustrative snapshot rather than a longitudinal trend • Because sFlt-1 alone can be influenced by other factors (gestational age, multiple gestation, renal function), it is more informative when interpreted alongside PlGF as a ratio rather than in isolation — the motivation for Stage 4
sFlt-1 should be understood functionally, not just as "a marker that goes up" — it directly antagonizes the pro-angiogenic signaling maternal vessels depend on, giving a mechanistic explanation for why its elevation tracks with the vascular manifestations of preeclampsia.
Placental growth factor (PlGF), a member of the VEGF family produced predominantly by placental trophoblast, is the pro-angiogenic counterweight to sFlt-1. Under normal conditions PlGF supports endothelial proliferation, vasodilation, and healthy placental vascular development, and its concentration typically rises through most of pregnancy. In preeclampsia, PlGF concentrations are characteristically lower than expected for gestational age — moving in the opposite direction from sFlt-1 and compounding the anti-angiogenic shift.
Biological role of PlGF: • PlGF binds Flt-1 (and, weakly, VEGFR-2-related pathways) to promote endothelial cell proliferation, migration, and vasodilation • Under normal pregnancy physiology, free PlGF concentration rises through the first and second trimesters, peaking around mid-pregnancy before gradually declining toward term • PlGF supports the low-resistance uteroplacental vascular bed established through healthy trophoblast invasion (Stage 1)
Why PlGF falls in preeclampsia: • Excess circulating sFlt-1 binds and sequesters free PlGF, lowering the measurable "free" fraction available to signal at endothelial receptors • Underlying placental dysfunction may also directly reduce PlGF production by stressed trophoblast tissue • The combined effect is a PlGF trajectory that falls below the expected reference range for gestational age — a deviation that becomes apparent before overt clinical signs in many cases
Interpreting PlGF in context: • A low PlGF value in isolation is influenced by gestational age, so reference ranges are typically gestational-age-adjusted in real clinical use (simplified here to a single illustrative slider) • Because sFlt-1 rises while PlGF falls, the two markers move in opposite directions during the same pathological process — an internally consistent signal that is more specific when the two values are combined rather than interpreted individually • This complementary, opposite-direction behavior is precisely what motivates combining sFlt-1 and PlGF into a single ratio, examined in Stage 4
PlGF is not simply "the other number" — its decline reflects sequestration by excess sFlt-1 and reduced production by stressed placental tissue, reinforcing from the pro-angiogenic side the same imbalance that sFlt-1 signals from the anti-angiogenic side.
Because sFlt-1 rises and PlGF falls through the same underlying pathological process, dividing one by the other amplifies the signal and improves diagnostic and short-term prognostic performance compared with either marker alone. The ratio compresses two noisy, gestational-age- and assay-dependent values into a single number that can be compared against illustrative clinical cutoffs — most usefully to help rule out preeclampsia developing imminently in patients presenting with suspected symptoms, reducing unnecessary hospitalization while flagging those who need closer surveillance.
Mathematics of the ratio: • Ratio = sFlt-1 concentration ÷ PlGF concentration (both measured from the same maternal blood sample) • Because the two markers move in opposite directions during placental dysfunction, the ratio changes more than either component alone — a rising numerator and a falling denominator compound multiplicatively • This amplification improves separation between lower-risk and higher-risk patients compared with either sFlt-1 or PlGF interpreted in isolation
Why this particular combination is useful clinically: • Single-marker measurements are affected by pre-analytical and biological variability (assay platform, gestational age, maternal renal function, multiple gestation) • A ratio is somewhat self-normalizing: a woman with generally elevated angiogenic-family proteins for benign reasons will tend to have both markers shifted, partially canceling out in the ratio • Illustrative cutoffs (as used in this simulation) are typically framed around short-term prediction — for example, a lower ratio being associated with a reduced likelihood of the syndrome developing within about one week, supporting a "rule-out" strategy in women presenting with suspected but unconfirmed preeclampsia
Limitations to keep in mind: • The ratio is a probabilistic screening aid, not a stand-alone diagnostic replacement for clinical assessment, blood pressure measurement, and urine protein testing • Cutoff values in real clinical use vary by assay platform, gestational age (early- versus late-onset), and whether the goal is ruling out or ruling in the diagnosis • This simulator uses simplified, illustrative thresholds and slider ranges purely to demonstrate the underlying diagnostic logic — not to represent a specific validated clinical assay
The clinical value of combining sFlt-1 and PlGF is best understood as amplification of an opposite-direction signal: because the two markers respond in mirror-image fashion to the same placental pathology, their ratio carries more diagnostic information than the sum of its parts.
In practice, the sFlt-1/PlGF ratio is used to stratify patients presenting with suspected preeclampsia into lower and higher short-term risk categories, informing how intensively they are monitored and how soon they are reassessed — rather than functioning as a final diagnosis on its own. A lower-risk result supports more conservative management with routine follow-up, while an elevated result prompts closer surveillance, more frequent reassessment, and readiness to escalate care if clinical signs progress.
How the ratio informs the care pathway:
1. Lower short-term risk (ratio at or below the illustrative rule-out cutoff): • Interpreted as preeclampsia being less likely to develop imminently • Supports routine outpatient follow-up rather than admission for observation • Reduces unnecessary hospitalization and resource use in women whose presenting symptoms are unlikely to represent evolving preeclampsia
2. Elevated risk (ratio above the illustrative cutoff): • Supports closer surveillance: more frequent blood pressure checks, symptom review, and laboratory reassessment • May prompt earlier specialist involvement, increased fetal surveillance, and planning discussions around timing of delivery if the pregnancy is at a viable gestational age • Higher ratio values correspond to a stronger anti-angiogenic shift and generally shorter recommended reassessment intervals
3. Integration with the overall clinical picture: • The ratio is one input among several — blood pressure trends, proteinuria, symptoms (headache, visual disturbance, epigastric pain), and laboratory markers of end-organ function all remain essential • A single ratio result is a snapshot; trends over serial testing carry additional information not captured by this simulator • Risk stratification tools like this are designed to support clinical judgment and triage decisions, not to be applied mechanically as a stand-alone diagnostic rule
Why short-term stratification is the primary value proposition: • The strongest evidence for the sFlt-1/PlGF ratio lies in short-term prediction (days to about one week) in women presenting with suspected but unconfirmed preeclampsia • This time horizon aligns well with real clinical decisions: whether to admit now, reassess in days, or manage as outpatient with routine follow-up • Longer-horizon prediction and use as a universal screening test earlier in pregnancy remain active areas of ongoing clinical research and are outside the scope of this simplified illustrative tool
The clinical power of the sFlt-1/PlGF ratio lies less in a single cutoff number and more in how efficiently it helps allocate monitoring intensity — sparing lower-risk women unnecessary intervention while directing closer attention to those whose biochemistry signals a genuine anti-angiogenic shift.