Placenta accreta spectrum: imaging and diagnosis

M R C O G PA R T 2 · S O S P O C K E T C A R D · K N O W L E D G E A R E A 5 – A N T E N ATA L C A R E

Placenta Accreta Spectrum: Imaging and Diagnosis Self A, Cavallaro A, Collins SL. Placenta accreta spectrum: imaging and diagnosis. TOG 2025;27:15–28. doi:10.1111/tog.12956

1.7/10,000 67% 24–28 wk UK PAS INCIDENCE (2012) PAS RISK: PRAEVIA + ≥5 CAESAREANS SPECIALIST PLACENTAL ASSESSMENT

DO N' T-M IS S FA C TS

  1. Imaging is a screening tool, not a diagnostic test — never perform hysterectomy on antenatal suspicion alone

  2. Praevia + previous caesareans → PAS risk 3% / 11% / 40% / 61% / 67% (1–5+ caesareans)

  3. Scan asymptomatic women after 24 weeks, ideally reviewed by a specialist by 28 weeks; bleeding or preterm risk → review sooner

  4. Bladder 200–300 mL minimum; avoid excess probe pressure (falsely obliterates clear zone and thins myometrium)

  5. Lacunar flow >10 cm/s favours PAS; low/no flow favours lakes and uterine dehiscence

  6. PAS-only signs vs UD: bridging vessels, bladder wall interruption (‘=’ sign), uterovesical/subplacental hypervascularity, intracervical lakes

  7. MRI is not a routine adjunct — use only after expert ultrasound if ambiguity remains; no contrast, slices ≥5 mm

  8. Never use methotrexate for PAS — no evidence; pancytopenia, nephrotoxicity, reported maternal death

  9. Refer to a designated PAS centre; if PAS is found unexpectedly at surgery, consider closing the abdomen before hysterotomy and transferring

RULE-OUT VS RULE-IN SIGNS

Rule OUT (reassuring): visible clear zone · positive separation sign

Rule IN (worrying): placental bulge · bridging vessels · myometrium <1 mm · loss of clear zone

Unreliable alone: hypervascularity · lacunae · irregular bladder wall (all common in normal placentas)

FIGO CLINICAL GRADES

1 — adherent (accreta): no bulge, no neovascularity 2 — increta: bulge, hypervascularity, ‘dimple sign’

3a — percreta to serosa, plane preserved 3b — bladder invasion, no plane 3c — other pelvic organs/broad ligament/vagina

ABBREVIATION KEY

PAS — placenta accreta spectrum US — ultrasound

UD — uterine dehiscence 2D / 3D — two-dimensional / three-dimensional

EVT — extravillous trophoblast SC — stratum compactum

MDT — multidisciplinary team AV — arteriovenous

FIGO — International Federation of Gynecology and Obstetrics PPH — postpartum haemorrhage

EW-AIP — European Working Group on Abnormally Invasive GA — gestational age Placenta BMI — body mass index IS-PAS — International Society for Placenta Accreta Spectrum PRF — pulse repetition frequency MRI — magnetic resonance imaging RCOG — Royal College of Obstetricians and Gynaecologists

Source: The Obstetrician & Gynaecologist (TOG), RCOG journal — doi:10.1111/tog.12956

Clinically reviewed by NHS obstetricians and gynaecologists

MRCOG AI is an independent educational tool. It is not affiliated with, endorsed by, or connected to the Royal College of Obstetricians and Gynaecologists (RCOG).

Included with a Pass Package

Start free