Placenta Accreta Spectrum

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Classifications

Harrison's Part

◆

Subtypes

3

Placenta creta (accreta vera)

Villi adhere directly to the myometrial surface without an intervening decidual plane. Corresponds to superficial damage to the endometrium-myometrial interface. Absence of the decidua on histology was the traditional diagnostic criterion, but the same group has since called that reliance inadequate and possibly misleading and now directs pathologists to deep villous attachment within scar tissue and distortion of the uteroplacental interface with thick fibrinoid deposition; the criterion is therefore recorded here as contested rather than settled.

Show evidence (2 references)

PMID:28599899 SUPPORT Other

"Superficial damage leads primarily to an abnormally adherent placenta, and is diagnosed as the complete or partial absence of the decidua on histology."

Defines the superficial, adherent end of the spectrum and the historical histological criterion.

PMID:41485847 REFUTE Other

"Traditional reliance on the absence of the decidua basalis with villous tissue simply apposed to the superficial myometrium to confirm the diagnosis of accreta placentation at histopathologic examination is inadequate and possibly misleading."

Same first author, eight years later, explicitly retiring the histological criterion quoted from PMID:28599899 above. Recorded as REFUTE against the diagnostic-criterion claim, not against the existence of the adherent subtype; the source redirects diagnosis to deep villous attachment within scar tissue and distortion of the uteroplacental interface with thick fibrinoid deposition.

Placenta increta

Villous tissue extends into the thickness of the myometrium.

Show evidence (1 reference)

PMID:28599899 SUPPORT Other

"Placenta accreta spectrum was separated by pathologists into 3 categories: placenta creta when the villi simply adhere to the myometrium, placenta increta when the villi invade the myometrium, and placenta percreta where the villi invade the full thickness of the myometrium."

Establishes the three-tier pathological grading in which increta is the intermediate depth.

Placenta percreta

Classically defined as villous tissue traversing the full myometrial thickness to reach the serosa and adjacent pelvic organs. IMPORTANT: this grade is contested. Recent work argues that apparent percreta reflects surgical extrusion of placental tissue through a dehiscent lower uterine segment rather than true transmural invasion, and that there is no evidence villous tissue can cross the entire uterine wall. Retained here because it remains in universal clinical and pathological use, with the dispute recorded in the alternative hypothesis group.

Show evidence (2 references)

PMID:28599899 SUPPORT Other

"Placenta accreta spectrum was separated by pathologists into 3 categories: placenta creta when the villi simply adhere to the myometrium, placenta increta when the villi invade the myometrium, and placenta percreta where the villi invade the full thickness of the myometrium."

Documents the conventional definition of the percreta grade.

PMID:41485847 REFUTE Other

"Similarly, there is no evidence that villous tissue and extravillous trophoblastic cells can cross the entire uterine wall in accreta areas."

Directly disputes the transmural-invasion definition on which the percreta grade rests, supporting the surgical-extrusion alternative recorded below.

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Mechanistic Hypotheses

2

Absent-Decidua Permissive Model

absent_decidua_permissive_model CANONICAL

Evidence balance 2 support

PAS results from the ABSENCE OF A CONSTRAINT rather than from a gain of invasive capacity. Where a caesarean scar has failed to re-epithelialise, there is no decidua basalis and no intact endometrium-myometrial interface. The decidual and myometrial signals that normally arrest extravillous trophoblast migration at a defined depth are therefore missing, and structurally normal trophoblast attaches to and proceeds into the myometrium. On this model the trophoblastic changes seen in PAS specimens are a consequence of the abnormal myometrial environment, not a cause of the disorder.

This is the model that both cited authorities endorse, and it has a clear therapeutic and preventive corollary: PAS is primarily preventable by reducing primary caesarean rates and by scar-healing quality, not by targeting trophoblast biology. It also makes PAS the conceptual inverse of preeclampsia - the same interface, with the constraint removed rather than the invasion impaired.

Pathograph links

Uterine Scar and Endometrium-Myometrial Interface Damage -> Absent or Deficient Decidua Basalis DIRECT A non-re-epithelialised scar cannot support normal decidualisation at implantation, leaving the decidual layer absent or partial.

Absent or Deficient Decidua Basalis -> Unconstrained Trophoblast Attachment into Myometrium DIRECT With the decidual arrest signal missing, otherwise normal extravillous trophoblast attaches to and proceeds into myometrium.

Show evidence (2 references)

PMID:41485847 SUPPORT Other

"Placenta accreta spectrum is the consequence of placental development at sites where the normal decidual and myometrial mechanisms limiting the migration of the extravillous trophoblastic cells are missing, rather than being due to inherently abnormally invasive villous tissue."

States the permissive, constraint-loss model in full and explicitly contrasts it with the intrinsic-invasiveness alternative.

PMID:28599899 SUPPORT Other

"The cellular changes in the trophoblast observed in placenta accreta spectrum are probably secondary to the unusual myometrial environment in which it develops, and not a primary defect of trophoblast biology leading to excessive invasion of the myometrium."

Independently places the trophoblast abnormalities downstream of the abnormal uterine environment, the central claim distinguishing this model from the overinvasion model.

Trophoblast Overinvasion Model (legacy, disputed)

trophoblast_overinvasion_model ⚠ DEPRECATED

⚠ Overturned model — shown for reference, not as current mechanism

DisMech records superseded hypotheses explicitly rather than deleting them, so that claims still circulating in reviews, textbooks and older diagnostic criteria can be checked against an assessment. This model is not part of the disease mechanism DisMech asserts.

Citation volume does not decide standing here. A hypothesis may retain more supporting than refuting citations simply because the supporting literature accumulated for decades before the refutation landed; where the two conflict, DisMech follows the more recent and more direct evidence. Supporting citations below are retained for the historical record.

Evidence balance 2 refute

The historical model held that PAS is caused by intrinsically hyperinvasive extravillous trophoblast that actively penetrates and, in percreta, traverses the uterine wall to reach bladder and pelvic sidewall. This framing generated the terms "abnormally invasive placenta" and "placenta percreta" and still shapes much clinical language. It is retained here explicitly as a refuted alternative because it remains widespread in the literature and because distinguishing it from the permissive model changes both what is worth studying (trophoblast biology versus scar healing) and how operative findings are interpreted.

Show evidence (2 references)

PMID:28599899 REFUTE Other

"The cellular changes in the trophoblast observed in placenta accreta spectrum are probably secondary to the unusual myometrial environment in which it develops, and not a primary defect of trophoblast biology leading to excessive invasion of the myometrium."

Explicitly rejects a primary trophoblast defect as the cause of PAS.

PMID:41485847 REFUTE Other

"We have recently questioned the concept of overinvasive placentation and placenta percreta, providing evidence that surgical manipulation of a dehiscent lower uterine segment covering a placenta previa is responsible for the extrusion of part of the placental tissue."

Offers an alternative explanation for the observations that motivated the overinvasion model, attributing apparent transmural placenta to intraoperative extrusion through a dehiscent segment.

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Discussions and Knowledge Gaps

2

Is placenta percreta a real biological entity - villous tissue traversing the full thickness of the uterine wall - or is it an operative artefact, in which surgical manipulation of a dehiscent lower uterine segment extrudes placental tissue that was never transmurally invasive?

KNOWLEDGE GAP OPEN gap_pas_percreta_invasion_versus_extrusion

Attached to

pathophysiology#Unconstrained Trophoblast Attachment into Myometrium has_subtypes#Percreta

This is not a semantic quibble. If percreta is genuine transmural invasion, the disorder has a biological gradient of invasiveness and the search for trophoblast-intrinsic determinants of depth is justified. If instead apparent percreta is produced intraoperatively by manipulating a dehiscent segment, then the entire spectrum is one lesion (absent decidua) of varying extent, the term "abnormally invasive placenta" is a misnomer, and surgical technique becomes a determinant of what pathologists subsequently report - a feedback loop that would also bias every observational series graded at operation. The two cited authorities take the same side of this dispute, so the entry currently records a one-sided literature; a curator should verify whether a substantive counter-position exists before treating the overinvasion model as settled-refuted rather than merely contested.

Proposed experiments

Preoperative imaging versus operative and histological findings in suspected percreta

prospective imaging-pathology correlation study

exp_pas_percreta_preoperative_imaging_versus_operative_findings

Prospectively compare high-resolution preoperative MRI and ultrasound assessment of myometrial and serosal integrity against intraoperative findings and whole-mount histology in suspected percreta, with the surgical approach (manipulation versus en-bloc hysterectomy without attempted separation) recorded as an exposure. If transmural villous tissue is demonstrable on imaging before any surgical manipulation, true invasion is supported; if apparent transmural placenta appears only in cases where the dehiscent segment was manipulated, the extrusion explanation is supported.

Decision criterion

Transmural villous tissue identified on pre-manipulation imaging and confirmed on whole-mount histology in cases managed without attempted separation would support genuine percreta. Its absence in that stratum, with apparent percreta confined to manipulated cases, would support the operative-artefact explanation.

Would support

pathophysiology#Unconstrained Trophoblast Attachment into Myometrium

Which specific decidual and myometrial signals normally arrest extravillous trophoblast migration at the inner myometrium, and are they simply absent over a caesarean scar or actively replaced by a permissive scar-tissue environment?

KNOWLEDGE GAP OPEN gap_pas_decidual_arrest_signal

Attached to

pathophysiology#Absent or Deficient Decidua Basalis pathophysiology#Unconstrained Trophoblast Attachment into Myometrium

The canonical model is stated at the level of "the normal decidual and myometrial mechanisms limiting migration are missing", but the identity of those mechanisms is not specified in the cited sources. Resolving them matters for two reasons. First, the same arrest machinery is the counterpart of the invasion-promoting programme that fails in preeclampsia, so a shared molecular account would connect the two disorders at one interface. Second, if scar tissue is actively permissive rather than merely deficient, scar-healing interventions after caesarean could plausibly reduce PAS risk, which pure absence of decidua would not suggest.

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Pathophysiology

5

Uterine Scar and Endometrium-Myometrial Interface Damage

Caesarean delivery, and less commonly curettage, manual placental removal, myomectomy or endometritis, damages the endometrium-myometrial interface. Where the scar fails to re-epithelialise, a permanent defect in the endometrial lining of the lower uterine segment persists, frequently accompanied by a niche or dehiscence. This is the necessary antecedent lesion, and it explains why PAS incidence has tracked the rise in caesarean rates.

Absent-Decidua Permissive Model

myometrial cell CL:0002366

myometrium UBERON:0001296

Downstream

Absent or Deficient Decidua Basalis A non-re-epithelialised scar cannot support normal decidualisation at implantation, leaving the decidual layer absent or partial.

Show evidence (2 references)

PMID:28599899 SUPPORT Other

"It is a relatively new disorder of placentation, and is the consequence of damage to the endometrium-myometrial interface of the uterine wall."

Establishes interface damage as the antecedent lesion of PAS.

PMID:28599899 SUPPORT Other

"Today, the main cause of placenta accreta spectrum is uterine surgery and, in particular, uterine scar secondary to cesarean delivery."

Identifies caesarean scarring as the dominant contemporary cause.

Absent or Deficient Decidua Basalis

Implantation over the scar occurs onto a surface lacking normal decidua. The decidua is not merely a passive interface: it supplies the paracrine and extracellular-matrix signals that arrest extravillous trophoblast migration at the inner third of the myometrium in normal pregnancy, and it provides the cleavage plane along which the placenta separates in the third stage of labour. Its absence removes both functions at once, which is why the same lesion produces both abnormal depth and failure of separation.

Absent-Decidua Permissive Model

extravillous trophoblast CL:0008036

decidualization GO:0046697 ↓ DECREASED

decidua UBERON:0002450

Downstream

Unconstrained Trophoblast Attachment into Myometrium With the decidual arrest signal missing, otherwise normal extravillous trophoblast attaches to and proceeds into myometrium.

Show evidence (2 references)

PMID:28599899 SUPPORT Other

"Superficial damage leads primarily to an abnormally adherent placenta, and is diagnosed as the complete or partial absence of the decidua on histology."

Supports decidual absence as the lesion underlying the adherent form of PAS. Note this source also frames it as the histological diagnostic criterion, a framing the REFUTE item below retires; the mechanistic claim modelled by this node is unaffected.

PMID:41485847 REFUTE Other

"Traditional reliance on the absence of the decidua basalis with villous tissue simply apposed to the superficial myometrium to confirm the diagnosis of accreta placentation at histopathologic examination is inadequate and possibly misleading."

Scoped REFUTE: it refutes the use of decidual absence as the confirmatory histopathologic criterion, not the loss-of-decidual-constraint mechanism this node encodes. The same paper states the permissive model this entry's canonical hypothesis rests on, so the two are consistent - what is retired is the diagnostic inference, and pathologists are redirected to deep villous attachment within scar tissue and distortion of the uteroplacental interface with thick fibrinoid deposition.

Unconstrained Trophoblast Attachment into Myometrium

Villous and extravillous trophoblast tissue becomes anchored within the myometrium and its circulation. On the canonical model this reflects loss of the normal depth-limiting constraint rather than an intrinsic increase in invasive capacity; the trophoblastic changes observed in PAS specimens are read as secondary adaptations to the abnormal myometrial environment. The depth reached defines the creta/increta/percreta grading.

extravillous trophoblast CL:0008036

trophoblast cell migration GO:0061450 ↕ DYSREGULATED

myometrium UBERON:0001296

Downstream

Failure of Placental Separation at Delivery Myometrially anchored placenta has no decidual cleavage plane and cannot detach after fetal delivery.

Massive Obstetric Haemorrhage Attempted separation of a myometrially anchored, hypervascular placenta tears the abnormal vasculature.

Show evidence (1 reference)

PMID:28599899 SUPPORT Other

"In the absence of endometrial reepithelialization of the scar area the trophoblast and villous tissue can invade deeply within the myometrium, including its circulation, and reach the surrounding pelvic organs."

States the causal step from failed scar re-epithelialisation to deep myometrial and vascular involvement.

Failure of Placental Separation at Delivery

In normal third-stage labour the placenta shears along the decidua spongiosa as the uterus contracts. With decidua absent, no cleavage plane exists: the placenta remains adherent, manual removal is impossible or piecemeal, and the attempt itself opens the abnormal placental bed vasculature. This node is the pivot between the developmental lesion and the acute clinical catastrophe.

myometrium UBERON:0001296

Downstream

Massive Obstetric Haemorrhage Retained, adherent placenta prevents haemostasis and drives torrential blood loss.

Show evidence (1 reference)

PMID:41485847 SUPPORT Other

"Accreta placentation is a clinicopathologic diagnosis at delivery when 1 or more placental lobules are abnormally attached into a myometrial scar or congenital defect requiring surgical removal."

Defines PAS at the point of delivery by abnormal attachment requiring surgical removal, i.e. failure of physiological separation.

Massive Obstetric Haemorrhage

Torrential haemorrhage from the placental bed is the proximate cause of the high maternal morbidity of PAS, driving transfusion, coagulopathy, peripartum hysterectomy, bladder and ureteric injury, intensive care admission and maternal death. Anticipation is the single largest modifier of outcome, which is why antenatal ultrasound diagnosis and delivery in a specialist centre are the core of management.

blood coagulation GO:0007596 ↕ DYSREGULATED

Show evidence (1 reference)

PMID:28599899 SUPPORT Other

"Placenta accreta spectrum is a complex obstetric complication associated with high maternal morbidity."

Establishes high maternal morbidity as the clinical endpoint of PAS. The specific haemorrhagic mechanism detailed in this node description would benefit from a dedicated citation.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

3

Blood 1

Maternal hemorrhage VERY_FREQUENT Abnormal bleeding HP:0001892

HPO has no obstetric or postpartum haemorrhage term. Bound to the general HP:0001892 Abnormal bleeding parent, which understates the severity and obstetric context; flagged as an HPO gap alongside the missing postpartum-haemorrhage term.

Show evidence (1 reference)

PMID:28599899 SUPPORT Other

"Placenta accreta spectrum is a complex obstetric complication associated with high maternal morbidity."

Supports high maternal morbidity. The snippet does not name haemorrhage specifically nor quantify its frequency; the VERY_FREQUENT band reflects general clinical description and needs a dedicated citation.

Other 2

Abnormally adherent placenta OBLIGATE

HPO does not provide a placenta accreta or adherent-placenta term; the entry is anchored on MONDO:0005916 at disease level instead, and no phenotype_term is asserted here rather than binding to a misleading parent. Flagged as an HPO gap.

Show evidence (1 reference)

PMID:41485847 SUPPORT Other

"Accreta placentation is a clinicopathologic diagnosis at delivery when 1 or more placental lobules are abnormally attached into a myometrial scar or congenital defect requiring surgical removal."

Supplies the clinicopathological definition used for this phenotype.

Placenta previa FREQUENT

Curated as an associated obstetric finding rather than a consequence: previa is part of the setting in which PAS develops. HPO provides no placenta previa term.

Show evidence (1 reference)

PMID:41485847 SUPPORT Other

"Over 90% of cases of placenta accreta spectrum are found in patients with a prior history of cesarean delivery presenting with a low-lying placenta or a placenta previa developing inside a lower uterine segment scar."

Documents the low-lying placenta / previa presentation in over 90% of cases.

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Medical Actions

3

Planned Cesarean Hysterectomy with the Placenta Left In Situ

Action: cesarean hysterectomy Ontology label: Hysterectomy NCIT:C15256

The generally accepted definitive management is delivery of the fetus by caesarean section followed by hysterectomy with the placenta left attached and undisturbed. It does not correct the adherent interface; it removes the organ that cannot separate, and specifically avoids the attempted manual removal that converts non-separation into torrential bleeding.

Mechanism Target:

BYPASSES Failure of Placental Separation at Delivery — Leaving the placenta in situ and removing the uterus with it works around the non-separating placental bed rather than attempting to restore separation, which the abnormal interface cannot support.

INHIBITS Massive Obstetric Haemorrhage — Avoiding placental disruption removes the proximate trigger of the terminal haemorrhage node; attempted removal is what precipitates it.

Show evidence (1 reference)

PMID:30461695 SUPPORT Other

"The most generally accepted approach to placenta accreta spectrum is cesarean hysterectomy with the placenta left in situ after delivery of the fetus (attempts at placental removal are associated with significant risk of hemorrhage)."

States both halves of the mechanism link modelled here - hysterectomy with the placenta left in situ as the accepted approach, and attempted placental removal as the step that precipitates haemorrhage. Classified as OTHER because this is a professional-society consensus document (ACOG/SMFM), not a primary study reporting its own data.

Planned Delivery in a Level III-IV Maternal Care Centre with a Multidisciplinary Team

Action: planned delivery in a specialist maternal care centre Ontology label: Obstetric Procedure NCIT:C89340

Where PAS is diagnosed antenatally, outcomes depend on where and how delivery is organised: a scheduled delivery before labour or bleeding, in a centre with a standing multidisciplinary PAS team. This is a care-organisation intervention rather than a drug, and it is the main modifiable determinant of maternal morbidity once the placental lesion is established.

Mechanism Target:

INHIBITS Massive Obstetric Haemorrhage — Delivering before the onset of labour or bleeding, and without placental disruption, pre-empts the terminal haemorrhage node rather than treating it after the fact.

Show evidence (2 references)

PMID:30461695 SUPPORT Other

"Antenatal diagnosis of placenta accreta spectrum is highly desirable because outcomes are optimized when delivery occurs at a level III or IV maternal care facility before the onset of labor or bleeding and with avoidance of placental disruption."

Ties the outcome benefit to the three components modelled in this treatment - level III/IV facility, delivery before labour or bleeding, and avoidance of placental disruption. OTHER because the source is a society consensus document.

PMID:30461695 SUPPORT Other

"Optimal management involves a standardized approach with a comprehensive multidisciplinary care team accustomed to management of placenta accreta spectrum."

Supports the multidisciplinary-team component specifically, which the first snippet does not name.

Massive Transfusion Protocol and Blood Bank Support

Action: massive transfusion protocol Ontology label: Blood Transfusion NCIT:C15192

Preparation for large-volume blood replacement is part of planned PAS delivery. Unlike the two treatments above this mitigates the consequences of haemorrhage rather than preventing it, so it deliberately carries no target_mechanisms edge into the pathograph.

Show evidence (1 reference)

PMID:30461695 SUPPORT Other

"access to a blood bank capable of employing massive transfusion protocols should help guide decisions about delivery location"

Establishes massive-transfusion capability as a required component of PAS delivery planning. OTHER because the source is a society consensus document.

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Environmental Factors

2

Previous caesarean delivery

The dominant modifiable risk factor and the reason PAS incidence has risen with caesarean rates. Risk increases with the number of prior caesarean deliveries.

Show evidence (1 reference)

PMID:28599899 SUPPORT Other

"Today, the main cause of placenta accreta spectrum is uterine surgery and, in particular, uterine scar secondary to cesarean delivery."

Identifies caesarean scar as the principal cause of contemporary PAS.

Uterine curettage, manual placental removal, or endometritis

The historically dominant causes, before caesarean delivery became the main route to interface damage. Still relevant in settings with lower caesarean rates.

Show evidence (1 reference)

PMID:28599899 SUPPORT Other

"When first described 80 years ago, it mainly occurred after manual removal of the placenta, uterine curettage, or endometritis."

Documents the historical causes of endometrium-myometrial interface damage.

🔬

Diagnosis

1

Antenatal ultrasound

Prenatal ultrasound is the principal diagnostic modality, and antenatal recognition is the main determinant of outcome because it permits planned delivery in a centre with surgical, transfusion and critical care capability. Numerous sonographic signs have been described over three decades; their evidence base and anatomical correlates are the subject of the cited review.

Show evidence (1 reference)

PMID:28599899 SUPPORT Other

"Several prenatal ultrasound signs of placenta accreta spectrum were reported over the last 35 years, principally the disappearance of the normal uteroplacental interface (clear zone), extreme thinning of the underlying myometrium, and vascular changes within the placenta (lacunae) and placental..."

Names the four established sonographic signs of PAS - loss of the clear zone, myometrial thinning, placental lacunae, and placental-bed hypervascularity - each of which is the imaging correlate of the interface damage modelled in the pathophysiology. The review does not itself report diagnostic accuracy for these signs, so this remains PARTIAL and a performance citation is still needed.

📊

Prevalence

1

Patients with placenta accreta spectrum, by obstetric history

Unknown Unknown

Not a population prevalence but a composition statistic: over 90% of PAS cases occur in patients with prior caesarean delivery presenting with a low-lying placenta or placenta previa in a lower uterine segment scar. Recorded here because the iatrogenic concentration of risk is the defining epidemiological feature of the disorder. A true population incidence record is still needed.

Show evidence (1 reference)

PMID:41485847 SUPPORT Other

"Over 90% of cases of placenta accreta spectrum are found in patients with a prior history of cesarean delivery presenting with a low-lying placenta or a placenta previa developing inside a lower uterine segment scar."

Quantifies the concentration of PAS in scarred, previa-complicated uteri.

{ }

Source YAML

click to show

name: Placenta Accreta Spectrum
creation_date: "2026-08-02T00:00:00Z"
category: Complex
synonyms:
- PAS
- Placenta accreta
- Morbidly adherent placenta
- Abnormally invasive placenta
description: >-
  Placenta accreta spectrum (PAS) is a disorder of placental attachment in which
  placental tissue is abnormally adherent to, or embedded within, the uterine wall
  and cannot separate at delivery, causing catastrophic obstetric haemorrhage. It is
  an iatrogenic epidemic: over 90% of cases arise in a uterus scarred by previous
  caesarean delivery, with the placenta implanting low, over the scar. The
  mechanistic core is not an intrinsically aggressive trophoblast but a missing
  brake - where the caesarean scar has failed to re-epithelialise, the decidua
  basalis is absent or deficient, so the normal decidual and myometrial mechanisms
  that limit extravillous trophoblast migration are simply not there, and otherwise
  normal placentation proceeds into the myometrium. Depth of attachment defines the
  historical pathological grades (creta, increta, percreta). PAS is the mechanistic
  counterpart of preeclampsia at the same maternal-fetal interface: preeclampsia is
  a failure of adequate trophoblast invasion into an intact decidua, whereas PAS is
  unimpeded attachment where the decidual barrier is absent.
disease_term:
  preferred_term: placenta accreta
  term:
    id: MONDO:0005916
    label: placenta accreta
parents:
- Placenta disorder
- Obstetric disorder
classifications:
  harrisons_chapter:
  - classification_value: OTHER
has_subtypes:
- name: Creta
  display_name: Placenta creta (accreta vera)
  description: >-
    Villi adhere directly to the myometrial surface without an intervening decidual
    plane. Corresponds to superficial damage to the endometrium-myometrial interface.
    Absence of the decidua on histology was the traditional diagnostic criterion, but
    the same group has since called that reliance inadequate and possibly misleading
    and now directs pathologists to deep villous attachment within scar tissue and
    distortion of the uteroplacental interface with thick fibrinoid deposition; the
    criterion is therefore recorded here as contested rather than settled.
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Superficial damage leads primarily to an abnormally adherent placenta, and is diagnosed as the complete or partial absence of the decidua on histology."
    explanation: Defines the superficial, adherent end of the spectrum and the historical histological criterion.
  - reference: PMID:41485847
    reference_title: "What is placenta accreta?"
    supports: REFUTE
    evidence_source: OTHER
    snippet: "Traditional reliance on the absence of the decidua basalis with villous tissue simply apposed to the superficial myometrium to confirm the diagnosis of accreta placentation at histopathologic examination is inadequate and possibly misleading."
    explanation: >-
      Same first author, eight years later, explicitly retiring the histological
      criterion quoted from PMID:28599899 above. Recorded as REFUTE against the
      diagnostic-criterion claim, not against the existence of the adherent subtype;
      the source redirects diagnosis to deep villous attachment within scar tissue and
      distortion of the uteroplacental interface with thick fibrinoid deposition.
- name: Increta
  display_name: Placenta increta
  description: Villous tissue extends into the thickness of the myometrium.
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Placenta accreta spectrum was separated by pathologists into 3 categories: placenta creta when the villi simply adhere to the myometrium, placenta increta when the villi invade the myometrium, and placenta percreta where the villi invade the full thickness of the myometrium."
    explanation: Establishes the three-tier pathological grading in which increta is the intermediate depth.
- name: Percreta
  display_name: Placenta percreta
  description: >-
    Classically defined as villous tissue traversing the full myometrial thickness to
    reach the serosa and adjacent pelvic organs. IMPORTANT: this grade is contested.
    Recent work argues that apparent percreta reflects surgical extrusion of placental
    tissue through a dehiscent lower uterine segment rather than true transmural
    invasion, and that there is no evidence villous tissue can cross the entire
    uterine wall. Retained here because it remains in universal clinical and
    pathological use, with the dispute recorded in the alternative hypothesis group.
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Placenta accreta spectrum was separated by pathologists into 3 categories: placenta creta when the villi simply adhere to the myometrium, placenta increta when the villi invade the myometrium, and placenta percreta where the villi invade the full thickness of the myometrium."
    explanation: Documents the conventional definition of the percreta grade.
  - reference: PMID:41485847
    reference_title: "What is placenta accreta?"
    supports: REFUTE
    evidence_source: OTHER
    snippet: "Similarly, there is no evidence that villous tissue and extravillous trophoblastic cells can cross the entire uterine wall in accreta areas."
    explanation: >-
      Directly disputes the transmural-invasion definition on which the percreta grade
      rests, supporting the surgical-extrusion alternative recorded below.
prevalence:
- population: Patients with placenta accreta spectrum, by obstetric history
  measure_type: UNKNOWN
  prevalence_class: UNKNOWN
  notes: >-
    Not a population prevalence but a composition statistic: over 90% of PAS cases
    occur in patients with prior caesarean delivery presenting with a low-lying
    placenta or placenta previa in a lower uterine segment scar. Recorded here
    because the iatrogenic concentration of risk is the defining epidemiological
    feature of the disorder. A true population incidence record is still needed.
  evidence:
  - reference: PMID:41485847
    reference_title: "What is placenta accreta?"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Over 90% of cases of placenta accreta spectrum are found in patients with a prior history of cesarean delivery presenting with a low-lying placenta or a placenta previa developing inside a lower uterine segment scar."
    explanation: Quantifies the concentration of PAS in scarred, previa-complicated uteri.
mechanistic_hypotheses:
- hypothesis_group_id: absent_decidua_permissive_model
  hypothesis_label: Absent-Decidua Permissive Model
  status: CANONICAL
  description: >-
    PAS results from the ABSENCE OF A CONSTRAINT rather than from a gain of invasive
    capacity. Where a caesarean scar has failed to re-epithelialise, there is no
    decidua basalis and no intact endometrium-myometrial interface. The decidual and
    myometrial signals that normally arrest extravillous trophoblast migration at a
    defined depth are therefore missing, and structurally normal trophoblast attaches
    to and proceeds into the myometrium. On this model the trophoblastic changes seen
    in PAS specimens are a consequence of the abnormal myometrial environment, not a
    cause of the disorder.
  notes: >-
    This is the model that both cited authorities endorse, and it has a clear
    therapeutic and preventive corollary: PAS is primarily preventable by reducing
    primary caesarean rates and by scar-healing quality, not by targeting trophoblast
    biology. It also makes PAS the conceptual inverse of preeclampsia - the same
    interface, with the constraint removed rather than the invasion impaired.
  evidence:
  - reference: PMID:41485847
    reference_title: "What is placenta accreta?"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Placenta accreta spectrum is the consequence of placental development at sites where the normal decidual and myometrial mechanisms limiting the migration of the extravillous trophoblastic cells are missing, rather than being due to inherently abnormally invasive villous tissue."
    explanation: >-
      States the permissive, constraint-loss model in full and explicitly contrasts it
      with the intrinsic-invasiveness alternative.
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The cellular changes in the trophoblast observed in placenta accreta spectrum are probably secondary to the unusual myometrial environment in which it develops, and not a primary defect of trophoblast biology leading to excessive invasion of the myometrium."
    explanation: >-
      Independently places the trophoblast abnormalities downstream of the abnormal
      uterine environment, the central claim distinguishing this model from the
      overinvasion model.
- hypothesis_group_id: trophoblast_overinvasion_model
  hypothesis_label: Trophoblast Overinvasion Model (legacy, disputed)
  status: DEPRECATED
  description: >-
    The historical model held that PAS is caused by intrinsically hyperinvasive
    extravillous trophoblast that actively penetrates and, in percreta, traverses the
    uterine wall to reach bladder and pelvic sidewall. This framing generated the
    terms "abnormally invasive placenta" and "placenta percreta" and still shapes much
    clinical language. It is retained here explicitly as a refuted alternative because
    it remains widespread in the literature and because distinguishing it from the
    permissive model changes both what is worth studying (trophoblast biology versus
    scar healing) and how operative findings are interpreted.
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: REFUTE
    evidence_source: OTHER
    snippet: "The cellular changes in the trophoblast observed in placenta accreta spectrum are probably secondary to the unusual myometrial environment in which it develops, and not a primary defect of trophoblast biology leading to excessive invasion of the myometrium."
    explanation: Explicitly rejects a primary trophoblast defect as the cause of PAS.
  - reference: PMID:41485847
    reference_title: "What is placenta accreta?"
    supports: REFUTE
    evidence_source: OTHER
    snippet: "We have recently questioned the concept of overinvasive placentation and placenta percreta, providing evidence that surgical manipulation of a dehiscent lower uterine segment covering a placenta previa is responsible for the extrusion of part of the placental tissue."
    explanation: >-
      Offers an alternative explanation for the observations that motivated the
      overinvasion model, attributing apparent transmural placenta to intraoperative
      extrusion through a dehiscent segment.
pathophysiology:
- name: Uterine Scar and Endometrium-Myometrial Interface Damage
  biological_scale: TISSUE
  description: >-
    Caesarean delivery, and less commonly curettage, manual placental removal,
    myomectomy or endometritis, damages the endometrium-myometrial interface. Where
    the scar fails to re-epithelialise, a permanent defect in the endometrial lining
    of the lower uterine segment persists, frequently accompanied by a niche or
    dehiscence. This is the necessary antecedent lesion, and it explains why PAS
    incidence has tracked the rise in caesarean rates.
  cell_types:
  - preferred_term: myometrial cell
    term:
      id: CL:0002366
      label: myometrial cell
  locations:
  - preferred_term: myometrium
    term:
      id: UBERON:0001296
      label: myometrium
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It is a relatively new disorder of placentation, and is the consequence of damage to the endometrium-myometrial interface of the uterine wall."
    explanation: Establishes interface damage as the antecedent lesion of PAS.
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Today, the main cause of placenta accreta spectrum is uterine surgery and, in particular, uterine scar secondary to cesarean delivery."
    explanation: Identifies caesarean scarring as the dominant contemporary cause.
  downstream:
  - target: Absent or Deficient Decidua Basalis
    description: >-
      A non-re-epithelialised scar cannot support normal decidualisation at
      implantation, leaving the decidual layer absent or partial.
    hypothesis_groups:
    - absent_decidua_permissive_model
    causal_link_type: DIRECT
- name: Absent or Deficient Decidua Basalis
  biological_scale: TISSUE
  description: >-
    Implantation over the scar occurs onto a surface lacking normal decidua. The
    decidua is not merely a passive interface: it supplies the paracrine and
    extracellular-matrix signals that arrest extravillous trophoblast migration at the
    inner third of the myometrium in normal pregnancy, and it provides the cleavage
    plane along which the placenta separates in the third stage of labour. Its
    absence removes both functions at once, which is why the same lesion produces both
    abnormal depth and failure of separation.
  cell_types:
  - preferred_term: extravillous trophoblast
    term:
      id: CL:0008036
      label: extravillous trophoblast
  locations:
  - preferred_term: decidua
    term:
      id: UBERON:0002450
      label: decidua
  biological_processes:
  - preferred_term: decidualization
    modifier: DECREASED
    term:
      id: GO:0046697
      label: decidualization
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Superficial damage leads primarily to an abnormally adherent placenta, and is diagnosed as the complete or partial absence of the decidua on histology."
    explanation: >-
      Supports decidual absence as the lesion underlying the adherent form of PAS. Note
      this source also frames it as the histological diagnostic criterion, a framing the
      REFUTE item below retires; the mechanistic claim modelled by this node is
      unaffected.
  - reference: PMID:41485847
    reference_title: "What is placenta accreta?"
    supports: REFUTE
    evidence_source: OTHER
    snippet: "Traditional reliance on the absence of the decidua basalis with villous tissue simply apposed to the superficial myometrium to confirm the diagnosis of accreta placentation at histopathologic examination is inadequate and possibly misleading."
    explanation: >-
      Scoped REFUTE: it refutes the use of decidual absence as the confirmatory
      histopathologic criterion, not the loss-of-decidual-constraint mechanism this node
      encodes. The same paper states the permissive model this entry's canonical
      hypothesis rests on, so the two are consistent - what is retired is the diagnostic
      inference, and pathologists are redirected to deep villous attachment within scar
      tissue and distortion of the uteroplacental interface with thick fibrinoid
      deposition.
  downstream:
  - target: Unconstrained Trophoblast Attachment into Myometrium
    description: >-
      With the decidual arrest signal missing, otherwise normal extravillous
      trophoblast attaches to and proceeds into myometrium.
    hypothesis_groups:
    - absent_decidua_permissive_model
    causal_link_type: DIRECT
- name: Unconstrained Trophoblast Attachment into Myometrium
  biological_scale: TISSUE
  description: >-
    Villous and extravillous trophoblast tissue becomes anchored within the myometrium
    and its circulation. On the canonical model this reflects loss of the normal
    depth-limiting constraint rather than an intrinsic increase in invasive capacity;
    the trophoblastic changes observed in PAS specimens are read as secondary
    adaptations to the abnormal myometrial environment. The depth reached defines the
    creta/increta/percreta grading.
  cell_types:
  - preferred_term: extravillous trophoblast
    term:
      id: CL:0008036
      label: extravillous trophoblast
  locations:
  - preferred_term: myometrium
    term:
      id: UBERON:0001296
      label: myometrium
  biological_processes:
  - preferred_term: trophoblast cell migration
    modifier: DYSREGULATED
    term:
      id: GO:0061450
      label: trophoblast cell migration
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "In the absence of endometrial reepithelialization of the scar area the trophoblast and villous tissue can invade deeply within the myometrium, including its circulation, and reach the surrounding pelvic organs."
    explanation: >-
      States the causal step from failed scar re-epithelialisation to deep myometrial
      and vascular involvement.
  downstream:
  - target: Failure of Placental Separation at Delivery
    description: >-
      Myometrially anchored placenta has no decidual cleavage plane and cannot detach
      after fetal delivery.
    causal_link_type: DIRECT
  - target: Massive Obstetric Haemorrhage
    description: >-
      Attempted separation of a myometrially anchored, hypervascular placenta tears
      the abnormal vasculature.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - disruption of enlarged subplacental and parametrial vessels
    - inability of the scarred lower segment to contract and achieve haemostasis
- name: Failure of Placental Separation at Delivery
  biological_scale: ORGANISM
  description: >-
    In normal third-stage labour the placenta shears along the decidua spongiosa as
    the uterus contracts. With decidua absent, no cleavage plane exists: the placenta
    remains adherent, manual removal is impossible or piecemeal, and the attempt
    itself opens the abnormal placental bed vasculature. This node is the pivot
    between the developmental lesion and the acute clinical catastrophe.
  locations:
  - preferred_term: myometrium
    term:
      id: UBERON:0001296
      label: myometrium
  evidence:
  - reference: PMID:41485847
    reference_title: "What is placenta accreta?"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Accreta placentation is a clinicopathologic diagnosis at delivery when 1 or more placental lobules are abnormally attached into a myometrial scar or congenital defect requiring surgical removal."
    explanation: >-
      Defines PAS at the point of delivery by abnormal attachment requiring surgical
      removal, i.e. failure of physiological separation.
  downstream:
  - target: Massive Obstetric Haemorrhage
    description: Retained, adherent placenta prevents haemostasis and drives torrential blood loss.
    causal_link_type: DIRECT
- name: Massive Obstetric Haemorrhage
  biological_scale: ORGANISM
  description: >-
    Torrential haemorrhage from the placental bed is the proximate cause of the high
    maternal morbidity of PAS, driving transfusion, coagulopathy, peripartum
    hysterectomy, bladder and ureteric injury, intensive care admission and maternal
    death. Anticipation is the single largest modifier of outcome, which is why
    antenatal ultrasound diagnosis and delivery in a specialist centre are the core of
    management.
  biological_processes:
  - preferred_term: blood coagulation
    modifier: DYSREGULATED
    term:
      id: GO:0007596
      label: blood coagulation
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Placenta accreta spectrum is a complex obstetric complication associated with high maternal morbidity."
    explanation: >-
      Establishes high maternal morbidity as the clinical endpoint of PAS. The specific
      haemorrhagic mechanism detailed in this node description would benefit from a
      dedicated citation.
phenotypes:
- name: Abnormally adherent placenta
  category: Obstetric
  frequency: OBLIGATE
  diagnostic: true
  description: >-
    Placental tissue attached into a myometrial scar or defect that will not separate
    spontaneously and requires surgical removal. This is the defining
    clinicopathological finding at delivery.
  notes: >-
    HPO does not provide a placenta accreta or adherent-placenta term; the entry is
    anchored on MONDO:0005916 at disease level instead, and no phenotype_term is
    asserted here rather than binding to a misleading parent. Flagged as an HPO gap.
  evidence:
  - reference: PMID:41485847
    reference_title: "What is placenta accreta?"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Accreta placentation is a clinicopathologic diagnosis at delivery when 1 or more placental lobules are abnormally attached into a myometrial scar or congenital defect requiring surgical removal."
    explanation: Supplies the clinicopathological definition used for this phenotype.
- name: Maternal hemorrhage
  category: Obstetric
  frequency: VERY_FREQUENT
  description: >-
    Massive peripartum blood loss, frequently requiring large-volume transfusion and
    peripartum hysterectomy.
  notes: >-
    HPO has no obstetric or postpartum haemorrhage term. Bound to the general
    HP:0001892 Abnormal bleeding parent, which understates the severity and obstetric
    context; flagged as an HPO gap alongside the missing postpartum-haemorrhage term.
  phenotype_term:
    preferred_term: Abnormal bleeding
    term:
      id: HP:0001892
      label: Abnormal bleeding
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Placenta accreta spectrum is a complex obstetric complication associated with high maternal morbidity."
    explanation: >-
      Supports high maternal morbidity. The snippet does not name haemorrhage
      specifically nor quantify its frequency; the VERY_FREQUENT band reflects general
      clinical description and needs a dedicated citation.
- name: Placenta previa
  category: Obstetric
  frequency: FREQUENT
  description: >-
    A low-lying placenta or placenta previa developing within the lower uterine
    segment scar is the typical antecedent presentation and the main prompt for
    antenatal PAS screening.
  notes: >-
    Curated as an associated obstetric finding rather than a consequence: previa is
    part of the setting in which PAS develops. HPO provides no placenta previa term.
  evidence:
  - reference: PMID:41485847
    reference_title: "What is placenta accreta?"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Over 90% of cases of placenta accreta spectrum are found in patients with a prior history of cesarean delivery presenting with a low-lying placenta or a placenta previa developing inside a lower uterine segment scar."
    explanation: Documents the low-lying placenta / previa presentation in over 90% of cases.
environmental:
- name: Previous caesarean delivery
  notes: >-
    The dominant modifiable risk factor and the reason PAS incidence has risen with
    caesarean rates. Risk increases with the number of prior caesarean deliveries.
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Today, the main cause of placenta accreta spectrum is uterine surgery and, in particular, uterine scar secondary to cesarean delivery."
    explanation: Identifies caesarean scar as the principal cause of contemporary PAS.
- name: Uterine curettage, manual placental removal, or endometritis
  notes: >-
    The historically dominant causes, before caesarean delivery became the main route
    to interface damage. Still relevant in settings with lower caesarean rates.
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "When first described 80 years ago, it mainly occurred after manual removal of the placenta, uterine curettage, or endometritis."
    explanation: Documents the historical causes of endometrium-myometrial interface damage.
diagnosis:
- name: Antenatal ultrasound
  description: >-
    Prenatal ultrasound is the principal diagnostic modality, and antenatal
    recognition is the main determinant of outcome because it permits planned delivery
    in a centre with surgical, transfusion and critical care capability. Numerous
    sonographic signs have been described over three decades; their evidence base and
    anatomical correlates are the subject of the cited review.
  evidence:
  - reference: PMID:28599899
    reference_title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Several prenatal ultrasound signs of placenta accreta spectrum were reported
      over the last 35 years, principally the disappearance of the normal
      uteroplacental interface (clear zone), extreme thinning of the underlying
      myometrium, and vascular changes within the placenta (lacunae) and placental
      bed (hypervascularity).
    explanation: >-
      Names the four established sonographic signs of PAS - loss of the clear zone,
      myometrial thinning, placental lacunae, and placental-bed hypervascularity -
      each of which is the imaging correlate of the interface damage modelled in the
      pathophysiology. The review does not itself report diagnostic accuracy for
      these signs, so this remains PARTIAL and a performance citation is still needed.
treatments:
- name: Planned Cesarean Hysterectomy with the Placenta Left In Situ
  description: >-
    The generally accepted definitive management is delivery of the fetus by
    caesarean section followed by hysterectomy with the placenta left attached and
    undisturbed. It does not correct the adherent interface; it removes the organ
    that cannot separate, and specifically avoids the attempted manual removal that
    converts non-separation into torrential bleeding.
  therapeutic_modality: SURGERY
  target_mechanisms:
  - target: Failure of Placental Separation at Delivery
    treatment_effect: BYPASSES
    description: >-
      Leaving the placenta in situ and removing the uterus with it works around the
      non-separating placental bed rather than attempting to restore separation,
      which the abnormal interface cannot support.
  - target: Massive Obstetric Haemorrhage
    treatment_effect: INHIBITS
    description: >-
      Avoiding placental disruption removes the proximate trigger of the terminal
      haemorrhage node; attempted removal is what precipitates it.
  treatment_term:
    preferred_term: cesarean hysterectomy
    term:
      id: NCIT:C15256
      label: Hysterectomy
  evidence:
  - reference: PMID:30461695
    reference_title: "Obstetric Care Consensus No. 7: Placenta Accreta Spectrum."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The most generally accepted approach to placenta accreta spectrum is cesarean hysterectomy with the placenta left in situ after delivery of the fetus (attempts at placental removal are associated with significant risk of hemorrhage)."
    explanation: >-
      States both halves of the mechanism link modelled here - hysterectomy with the
      placenta left in situ as the accepted approach, and attempted placental removal
      as the step that precipitates haemorrhage. Classified as OTHER because this is a
      professional-society consensus document (ACOG/SMFM), not a primary study
      reporting its own data.
- name: Planned Delivery in a Level III-IV Maternal Care Centre with a Multidisciplinary Team
  description: >-
    Where PAS is diagnosed antenatally, outcomes depend on where and how delivery is
    organised: a scheduled delivery before labour or bleeding, in a centre with a
    standing multidisciplinary PAS team. This is a care-organisation intervention
    rather than a drug, and it is the main modifiable determinant of maternal
    morbidity once the placental lesion is established.
  target_mechanisms:
  - target: Massive Obstetric Haemorrhage
    treatment_effect: INHIBITS
    description: >-
      Delivering before the onset of labour or bleeding, and without placental
      disruption, pre-empts the terminal haemorrhage node rather than treating it
      after the fact.
  treatment_term:
    preferred_term: planned delivery in a specialist maternal care centre
    term:
      id: NCIT:C89340
      label: Obstetric Procedure
  evidence:
  - reference: PMID:30461695
    reference_title: "Obstetric Care Consensus No. 7: Placenta Accreta Spectrum."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Antenatal diagnosis of placenta accreta spectrum is highly desirable because outcomes are optimized when delivery occurs at a level III or IV maternal care facility before the onset of labor or bleeding and with avoidance of placental disruption."
    explanation: >-
      Ties the outcome benefit to the three components modelled in this treatment -
      level III/IV facility, delivery before labour or bleeding, and avoidance of
      placental disruption. OTHER because the source is a society consensus document.
  - reference: PMID:30461695
    reference_title: "Obstetric Care Consensus No. 7: Placenta Accreta Spectrum."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Optimal management involves a standardized approach with a comprehensive multidisciplinary care team accustomed to management of placenta accreta spectrum."
    explanation: >-
      Supports the multidisciplinary-team component specifically, which the first
      snippet does not name.
- name: Massive Transfusion Protocol and Blood Bank Support
  description: >-
    Preparation for large-volume blood replacement is part of planned PAS delivery.
    Unlike the two treatments above this mitigates the consequences of haemorrhage
    rather than preventing it, so it deliberately carries no target_mechanisms edge
    into the pathograph.
  treatment_term:
    preferred_term: massive transfusion protocol
    term:
      id: NCIT:C15192
      label: Blood Transfusion
  evidence:
  - reference: PMID:30461695
    reference_title: "Obstetric Care Consensus No. 7: Placenta Accreta Spectrum."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "access to a blood bank capable of employing massive transfusion protocols should help guide decisions about delivery location"
    explanation: >-
      Establishes massive-transfusion capability as a required component of PAS
      delivery planning. OTHER because the source is a society consensus document.
discussions:
- discussion_id: gap_pas_percreta_invasion_versus_extrusion
  prompt: >-
    Is placenta percreta a real biological entity - villous tissue traversing the full
    thickness of the uterine wall - or is it an operative artefact, in which surgical
    manipulation of a dehiscent lower uterine segment extrudes placental tissue that
    was never transmurally invasive?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Unconstrained Trophoblast Attachment into Myometrium
  - has_subtypes#Percreta
  rationale: >-
    This is not a semantic quibble. If percreta is genuine transmural invasion, the
    disorder has a biological gradient of invasiveness and the search for
    trophoblast-intrinsic determinants of depth is justified. If instead apparent
    percreta is produced intraoperatively by manipulating a dehiscent segment, then the
    entire spectrum is one lesion (absent decidua) of varying extent, the term
    "abnormally invasive placenta" is a misnomer, and surgical technique becomes a
    determinant of what pathologists subsequently report - a feedback loop that would
    also bias every observational series graded at operation. The two cited authorities
    take the same side of this dispute, so the entry currently records a one-sided
    literature; a curator should verify whether a substantive counter-position exists
    before treating the overinvasion model as settled-refuted rather than merely
    contested.
  proposed_experiments:
  - experiment_id: exp_pas_percreta_preoperative_imaging_versus_operative_findings
    name: Preoperative imaging versus operative and histological findings in suspected percreta
    description: >-
      Prospectively compare high-resolution preoperative MRI and ultrasound assessment
      of myometrial and serosal integrity against intraoperative findings and
      whole-mount histology in suspected percreta, with the surgical approach
      (manipulation versus en-bloc hysterectomy without attempted separation)
      recorded as an exposure. If transmural villous tissue is demonstrable on imaging
      before any surgical manipulation, true invasion is supported; if apparent
      transmural placenta appears only in cases where the dehiscent segment was
      manipulated, the extrusion explanation is supported.
    experiment_type:
      preferred_term: prospective imaging-pathology correlation study
    decision_criterion: >-
      Transmural villous tissue identified on pre-manipulation imaging and confirmed on
      whole-mount histology in cases managed without attempted separation would support
      genuine percreta. Its absence in that stratum, with apparent percreta confined to
      manipulated cases, would support the operative-artefact explanation.
    would_support:
    - pathophysiology#Unconstrained Trophoblast Attachment into Myometrium
- discussion_id: gap_pas_decidual_arrest_signal
  prompt: >-
    Which specific decidual and myometrial signals normally arrest extravillous
    trophoblast migration at the inner myometrium, and are they simply absent over a
    caesarean scar or actively replaced by a permissive scar-tissue environment?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Absent or Deficient Decidua Basalis
  - pathophysiology#Unconstrained Trophoblast Attachment into Myometrium
  rationale: >-
    The canonical model is stated at the level of "the normal decidual and myometrial
    mechanisms limiting migration are missing", but the identity of those mechanisms is
    not specified in the cited sources. Resolving them matters for two reasons. First,
    the same arrest machinery is the counterpart of the invasion-promoting programme
    that fails in preeclampsia, so a shared molecular account would connect the two
    disorders at one interface. Second, if scar tissue is actively permissive rather
    than merely deficient, scar-healing interventions after caesarean could plausibly
    reduce PAS risk, which pure absence of decidua would not suggest.
references:
- reference: PMID:28599899
  title: "Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging."
- reference: PMID:41485847
  title: "What is placenta accreta?"
notes: >-
  Curation note on framing: an earlier draft of this entry described PAS as
  trophoblast "over-invasion", the mechanistic mirror of preeclampsia's
  under-invasion. Both cited authorities explicitly reject that framing, so the entry
  models the constraint-loss (absent decidua) account as CANONICAL and records
  overinvasion as a DEPRECATED legacy hypothesis (the schema's HypothesisStatusEnum
  has no REFUTED value; DEPRECATED is the closest available and the refuting evidence
  is attached to the hypothesis itself). The preeclampsia comparison is retained
  in the description but restated accurately: both are disorders of the same
  maternal-fetal interface, one from impaired invasion into intact decidua and the
  other from unimpeded attachment where decidua is absent.

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2

PMID:28599899

Placenta accreta spectrum: pathophysiology and evidence-based anatomy for prenatal ultrasound imaging.

No top-level findings curated for this source.

PMID:41485847

What is placenta accreta?

No top-level findings curated for this source.

Placenta Accreta Spectrum

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