Placenta Praevia

1. Clinical Overview

Placenta praevia is defined as a placenta that lies wholly or partially in the lower uterine segment, typically measured after 20 weeks of gestation. [1] It represents one of the most important causes of antepartum haemorrhage (APH) and is associated with significant maternal and perinatal morbidity and mortality. [2]

Modern Classification

The RCOG Green-top Guideline No. 27a (2018) has modernized the classification system, moving away from outdated grading systems (Grade I–IV or major/minor) toward descriptive ultrasound-based terminology: [1]

1. Low-Lying Placenta: The placental edge is within 20mm of the internal cervical os but does not cover it.
2. Placenta Praevia: The placenta covers the internal cervical os, either partially or completely.

This contemporary approach provides clearer clinical correlation and more accurate prognostication.

The Critical Association: Placenta Accreta Spectrum (PAS)

The combination of placenta praevia and previous caesarean section creates one of the highest-risk scenarios in obstetrics, with PAS risk escalating dramatically: [3]

• 1 prior caesarean: 11–25% PAS risk
• 2 prior caesareans: 40% PAS risk
• 3 prior caesareans: 61% PAS risk

This exponential increase underscores the importance of systematic ultrasound screening and multidisciplinary planning in all women with praevia and uterine scars.

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2. Epidemiology

Incidence and Temporal Trends

The incidence of placenta praevia has increased over recent decades, primarily driven by rising caesarean section rates worldwide. [6] A large meta-analysis demonstrated that women with a history of caesarean delivery have a 1.74-fold increased odds of placenta praevia in subsequent pregnancies. [6]

Placental Migration

Approximately 90% of low-lying placentas identified at the routine 20-week anomaly scan will resolve by 36 weeks through a process termed "placental migration." [5] This is not true migration but rather differential growth of the lower uterine segment, causing the placenta to appear to move away from the internal os. [7]

Factors reducing likelihood of resolution: [5,7]

• Complete placenta praevia (covering os)
• Posterior placental position
• Overlapping of os by ≥15mm
• Prior caesarean section
• Presence of placenta accreta spectrum features

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3. Pathophysiology

Abnormal Placental Implantation

┌─────────────────────────────────────────────────────────────────────────────┐
│                   PLACENTA PRAEVIA PATHOPHYSIOLOGY                          │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│   ┌─────────────────────────────────────────────────────────────────────┐   │
│   │              ABNORMAL IMPLANTATION IN LOWER SEGMENT                 │   │
│   │  • Low blastocyst implantation near internal os                     │   │
│   │  • Risk factors: Endometrial damage, multiparity, AMA               │   │
│   │  • Large placental mass (twins, smoking-induced hypoxia)            │   │
│   │  • Defective decidualization in scarred lower segment               │   │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                                    ↓                                        │
│   ┌─────────────────────────────────────────────────────────────────────┐   │
│   │           THIRD TRIMESTER: LOWER SEGMENT DEVELOPMENT                │   │
│   │  • Progressive thinning and expansion of lower uterine segment      │   │
│   │  • Cervical effacement begins (term approaches)                     │   │
│   │  • Mechanical stretching creates shearing forces                    │   │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                                    ↓                                        │
│   ┌─────────────────────────────────────────────────────────────────────┐   │
│   │                  PLACENTAL-DECIDUAL SEPARATION                      │   │
│   │  • Micro-separations at placental margin                            │   │
│   │  • Spiral arteriole disruption → maternal bleeding                  │   │
│   │  • Lower segment myometrium CANNOT contract effectively             │   │
│   │    (unlike fundal "living ligature" mechanism)                      │   │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                                    ↓                                        │
│   ┌─────────────────────────────────────────────────────────────────────┐   │
│   │                  ANTEPARTUM HAEMORRHAGE (APH)                       │   │
│   │  • PAINLESS vaginal bleeding (hallmark feature)                     │   │
│   │  • Blood is maternal in origin (not fetal)                          │   │
│   │  • "Sentinel bleed": Often minor initial bleed → major bleed later  │   │
│   │  • Uterus remains soft, non-tender (vs. woody in abruption)         │   │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                                                                             │
└─────────────────────────────────────────────────────────────────────────────┘

The fundamental pathophysiological issue is that the lower uterine segment is poorly suited for placental attachment. [8] Unlike the fundus, the lower segment:

• Has thinner myometrium with reduced contractility
• Undergoes greater mechanical deformation in late pregnancy
• Contains fewer spiral arterioles with less robust remodeling

When placental separation occurs, the lower segment cannot generate sufficient muscle contraction to compress torn vessels ("physiological ligature"), leading to potentially life-threatening haemorrhage. [8]

Molecular and Cellular Mechanisms

Recent research has elucidated that abnormal trophoblast invasion plays a central role. [9] In women with previous uterine surgery, Cesarean scar defects show:

• Deficient decidualization
• Reduced expression of matrix metalloproteinases (MMPs)
• Abnormal vascular remodeling
• Excessive trophoblast invasion (when placenta implants over scar) → PAS

These findings explain why caesarean section is the strongest modifiable risk factor for both placenta praevia and its most dangerous complication, placenta accreta spectrum. [3]

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4. Risk Factors

Established Risk Factors with Relative Risks

Mechanism of Increased Risk

Previous Caesarean Section: The caesarean scar creates an area of endometrial atrophy and fibrosis. [9] The blastocyst may preferentially implant in the lower segment if the fundal endometrium is scarred or if there is abnormal uterine vascularization.

Multiparity: Repeated pregnancies cause progressive endometrial atrophy, particularly in the fundus, encouraging lower implantation. [8]

Smoking: Causes placental hypertrophy secondary to chronic hypoxia, increasing placental surface area and likelihood of extending into the lower segment. [10]

Advanced Maternal Age: Associated with cumulative endometrial damage and vascular insufficiency, both favouring low implantation. [10]

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5. Clinical Presentation

Classical Presentation

The hallmark of placenta praevia is painless, bright red vaginal bleeding in the late second or third trimester. [1,2]

Typical features:

• Painless bleeding (contrasts sharply with placental abruption)
• Usually unprovoked (though may follow intercourse or vaginal examination)
• Often recurrent ("sentinel bleed" followed by heavier episodes)
• Uterus remains soft and non-tender
• Fetal heart rate typically normal (unless maternal shock develops)
• High presenting part or abnormal lie (breech, transverse) due to placenta preventing engagement

Sentinel Bleed Phenomenon

Approximately 70–80% of women with placenta praevia experience an initial minor bleeding episode before a larger haemorrhage. [1,12] This "warning bleed" typically occurs between 28–34 weeks and should never be dismissed—it mandates urgent assessment and planning.

Differential Diagnosis: Praevia vs. Abruption

Incidental/Asymptomatic Diagnosis

In modern practice, many cases (40–60%) are diagnosed incidentally on routine second-trimester ultrasound before any bleeding occurs. [1,4] These women require structured follow-up but can often be managed as outpatients if they remain asymptomatic.

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6. Investigations and Diagnosis

Transvaginal Ultrasound: The Gold Standard

Transvaginal ultrasound (TVUS) is the definitive investigation for diagnosing placenta praevia and is safe in the presence of bleeding. [1,13]

Key Points:

• Sensitivity: 87.5% (vs. 46.2% for transabdominal ultrasound)
• Specificity: 98.8% [13]
• Safety: The probe is positioned 2–3 cm from the cervix and does not provoke bleeding [13]
• Measurement: Distance from placental edge to internal os is precisely measured
• Superiority: Transabdominal scans are frequently limited by maternal body habitus, fetal position, and acoustic shadowing from the pubic bone

Ultrasound Criteria and Reporting

Modern RCOG guidelines recommend descriptive reporting: [1]

Additional measurements to report:

• Distance from placental edge to os (in mm)
• Placental location (anterior/posterior/lateral)
• Presence of placental lacunae (suggests PAS)
• Loss of retroplacental "clear zone" (suggests PAS)
• Bladder wall vascularity (Color Doppler for PAS screening)

Screening for Placenta Accreta Spectrum (PAS)

All women with placenta praevia AND prior caesarean section require systematic assessment for PAS. [1,3]

Ultrasound features suggestive of PAS: [3,14]

• Multiple placental lacunae ("Swiss cheese" appearance)
• Loss of retroplacental clear zone
• Thinning (less than 1mm) or disruption of uterine-bladder interface
• Bladder wall irregularity
• Increased subplacental vascularity on Color Doppler
• Placental bulge beyond uterine serosa (percreta)
• Bridging vessels extending into bladder (percreta)

MRI indications: [3]

• Posterior placenta (difficult to assess with ultrasound)
• Suspected percreta
• Planning surgical approach (delineates anatomy for multidisciplinary team)

Follow-Up Ultrasound Protocol (RCOG)

┌─────────────────────────────────────────────────────────────────────────────┐
│                   RCOG ULTRASOUND FOLLOW-UP PROTOCOL                        │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│   20-WEEK ANOMALY SCAN: Low-lying placenta or praevia detected             │
│                          ↓                                                  │
│   ┌─────────────────────────────────────────────────────────────────────┐   │
│   │                      32-WEEK RESCAN (TVUS)                          │   │
│   │  • Assess placental position                                        │   │
│   │  • Measure distance from os                                         │   │
│   │  • If ≥20mm from os → Discharge to normal care (vaginal delivery OK)│   │
│   │  • If less than 20mm → Arrange 36-week scan                                  │   │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                          ↓ (if still low)                                   │
│   ┌─────────────────────────────────────────────────────────────────────┐   │
│   │                      36-WEEK RESCAN (TVUS)                          │   │
│   │  • Final determination of placental position                        │   │
│   │  • ≥20mm from os → Vaginal delivery permitted                       │   │
│   │  • 10–20mm → Consultant decision (often trial of labor)             │   │
│   │  • less than 10mm or covering os → Elective caesarean section                │   │
│   │  • Plan delivery timing and mode                                    │   │
│   │  • Screen for PAS if prior CS                                       │   │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                                                                             │
└─────────────────────────────────────────────────────────────────────────────┘

Approximately 90% of low-lying placentas at 20 weeks will resolve by 36 weeks, particularly anterior placentas without prior caesarean section. [5,7]

Other Investigations

Laboratory Investigations (at presentation with bleeding):

• Full blood count (Hb, haematocrit, platelets)
• Group and save (G&S) → Cross-match 4 units if bleeding is significant
• Coagulation screen (if massive haemorrhage or abruption suspected)
• Kleihauer test (quantify fetomaternal haemorrhage in Rh-negative women)

Cardiotocography (CTG):

• Assess fetal wellbeing
• Monitor for contractions (may provoke bleeding if cervix dilating)

DO NOT perform:

• Digital vaginal examination until placenta praevia has been excluded by ultrasound (risk of catastrophic haemorrhage) [1,2]
• Speculum examination is safe and may identify other bleeding sources (cervical ectropion, polyp), but placental position must be known first

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7. Management

Acute Management of Antepartum Haemorrhage

Women presenting with vaginal bleeding and known or suspected placenta praevia require immediate assessment following the ABCDE approach. [1,2]

Emergency Protocol

┌─────────────────────────────────────────────────────────────────────────────┐
│              ACUTE APH MANAGEMENT IN PLACENTA PRAEVIA                       │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│   IMMEDIATE ACTIONS (first 15 minutes)                                      │
│   ┌─────────────────────────────────────────────────────────────────────┐   │
│   │  • Call for senior obstetric and anaesthetic help                   │   │
│   │  • ABC assessment: Airway, Breathing, Circulation                   │   │
│   │  • Two large-bore IV cannulae (14G or 16G)                          │   │
│   │  • Bloods: FBC, G&S, cross-match 4 units, coagulation               │   │
│   │  • Commence IV crystalloid resuscitation                            │   │
│   │  • Continuous CTG monitoring                                        │   │
│   │  • Avoid vaginal examination                                        │   │
│   │  • Transvaginal ultrasound to confirm placental position            │   │
│   └─────────────────────────────────────────────────────────────────────┘   │
│                                    ↓                                        │
│   SEVERITY STRATIFICATION                                                   │
│   ┌───────────────────────────┐       ┌─────────────────────────────────┐   │
│   │   MINOR BLEEDING          │       │   MAJOR/MASSIVE BLEEDING        │   │
│   │   • Haemodynamically      │       │   • Shock (HR > 110, BP less than 90)     │   │
│   │     stable                │       │   • Ongoing heavy bleeding      │   │
│   │   • Bleeding settling     │       │   • Fetal distress              │   │
│   │   • Fetal wellbeing OK    │       │   • Estimated loss > 1000mL      │   │
│   └───────────────────────────┘       └─────────────────────────────────┘   │
│            ↓                                      ↓                          │
│   ┌───────────────────────────┐       ┌─────────────────────────────────┐   │
│   │   CONSERVATIVE MANAGEMENT │       │   EMERGENCY DELIVERY            │   │
│   │   • Admit to hospital     │       │   • Activate obstetric emergency│   │
│   │   • IV access maintained  │       │     protocol (Code Red)         │   │
│   │   • Corticosteroids if    │       │   • Activate massive transfusion│   │
│   │     less than 34+6 weeks           │       │   • Emergency caesarean section │   │
│   │   • MgSO4 if less than 30 weeks    │       │     (may require classical      │   │
│   │   • Anti-D if Rh negative │       │     incision/vertical incision) │   │
│   │   • Observe 24-48h minimum│       │   • Senior surgeon + anaesthetist│   │
│   │   • Consider elective CS  │       │   • Cell salvage + cross-match  │   │
│   │     at 36-37 weeks        │       │   • Warn of hysterectomy risk   │   │
│   └───────────────────────────┘       └─────────────────────────────────┘   │
│                                                                             │
└─────────────────────────────────────────────────────────────────────────────┘

Antenatal Management (Asymptomatic or Post-Stabilisation)

Outpatient vs. Inpatient Care

Outpatient management is appropriate for asymptomatic women with placenta praevia if: [1,12]

• No history of bleeding
• Living within 15–20 minutes of hospital
• Reliable transport available 24/7
• Telephone access
• Good understanding of warning signs
• Compliance with pelvic rest advice

Inpatient admission is recommended if: [1]

• Any bleeding episode (even if minor)
• Lives > 20 minutes from hospital
• Poor social support
• Previous significant bleeding
• Additional risk factors (twins, suspected PAS)

Interventions During Antenatal Period

1. Pelvic Rest:

• Avoid sexual intercourse
• Avoid vigorous exercise
• Avoid activities that increase intra-abdominal pressure

2. Corticosteroids:

• Administer betamethasone 12mg IM × 2 doses (24h apart) if less than 34+6 weeks and risk of preterm delivery [1]

3. Magnesium Sulphate:

• Neuroprotection: 4g IV bolus + infusion if delivery anticipated less than 30 weeks [1]

4. Anti-D Immunoglobulin:

• Minimum 500 IU IM for all Rh-negative women after bleeding episode
• Kleihauer test to determine if additional dose needed
• Repeat every 6 weeks if ongoing bleeding/risk [1]

5. Iron Supplementation:

• Oral iron supplementation to optimize haemoglobin
• Target Hb > 100 g/L prior to elective delivery
• IV iron if oral not tolerated or inadequate response

6. Avoid Tocolysis:

• Tocolytics are generally not recommended for women in preterm labor with placenta praevia due to bleeding risk [1]

Delivery Planning

Timing of Elective Caesarean Section

Delivery timing balances the risk of prematurity against the risk of emergency delivery due to haemorrhage. [1,15]

RCOG Recommendations: [1]

A large retrospective study (n=102) found that uncomplicated placenta praevia delivered at 36–37 weeks had optimal neonatal outcomes without excessive bleeding risk. [15]

Mode of Delivery

Caesarean section is mandatory for placenta praevia covering the internal os. [1,2]

Vaginal delivery may be considered if:

• Placental edge is ≥20mm from internal os [1]
• Consultant obstetrician approval
• Continuous intrapartum monitoring
• Cross-matched blood immediately available
• Theatre and anaesthetic team on immediate standby
• Woman fully counselled about emergency caesarean risk

For low-lying placentas (10–20mm), decision-making is individualized based on parity, placental position, and clinical judgment.

Surgical Considerations

Pre-operative Preparation:

• Senior obstetrician (consultant or experienced registrar)
• Senior anaesthetist (consultant or equivalent)
• Cross-match 4–6 units of packed red cells
• Blood products available (FFP, platelets, cryoprecipitate)
• Cell salvage equipment (autologous blood transfusion)
• Inform neonatal team
• Vertical skin incision may be required if anterior placenta praevia
• Consent discussion: Risk of haemorrhage, hysterectomy, bladder injury

Anaesthesia:

• Regional anaesthesia (spinal/epidural) is preferred over general anaesthesia for elective caesarean in stable patients [1,16]
• Reduced maternal morbidity (aspiration risk, failed intubation)
• Immediate skin-to-skin contact
• Convert to GA if massive haemorrhage develops

Surgical Technique:

• Incision may need to be through placenta if anterior praevia → rapid delivery, clamp cord, deliver placenta
• Manual removal of placenta often required (poorly contracted lower segment)
• Oxytocin 5 IU IV bolus + 40 IU infusion
• Additional uterotonics: Ergometrine, carboprost, misoprostol
• Compression sutures (B-Lynch, Cho) if atonic PPH
• Intrauterine balloon tamponade (Bakri balloon)
• Interventional radiology (uterine artery embolization) if available
• Hysterectomy if uncontrollable bleeding (particularly with PAS)

Risk of Caesarean Hysterectomy:

• Placenta praevia alone: 5% [1]
• Placenta praevia + 1 prior CS: 10% [3]
• Placenta praevia + confirmed PAS: 50–70% [3]

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8. Placenta Accreta Spectrum (PAS)

Definition and Classification

Placenta accreta spectrum (PAS) refers to abnormal placental adherence to or invasion through the uterine wall, occurring when trophoblast invasion extends beyond the normal boundary (decidua basalis). [3,14]

Classification:

• Placenta Accreta (Vera): Chorionic villi attach to myometrium (absent decidua basalis) – 75% of cases
• Placenta Increta: Chorionic villi invade into myometrium – 18% of cases
• Placenta Percreta: Chorionic villi penetrate through serosa into adjacent organs (bladder, bowel) – 7% of cases

Epidemiology and Risk

The incidence of PAS has increased 10-fold over the past 50 years, mirroring the rise in caesarean section rates. [3] Current incidence is approximately 1 in 500 pregnancies. [3]

Highest-Risk Group:

• Placenta praevia + 3 prior caesarean sections = 61% risk of PAS [3]

Clinical Presentation

Many cases of PAS are asymptomatic and detected antenatally on ultrasound screening. [3,14]

When symptomatic:

• Persistent bleeding despite tocolysis or bed rest
• Failure of placental separation at third stage of labor (if undiagnosed)
• Massive postpartum haemorrhage with hypotension and shock

Diagnosis

Ultrasound findings: [14]

• Lacunae (irregular vascular spaces within placenta)
• Loss of clear zone (absent hypoechoic retroplacental zone)
• Thinning of myometrium overlying placenta (less than 1mm)
• Bladder wall irregularity
• Placental bulge (extension beyond uterine serosa)
• Increased vascularity (turbulent flow on Color Doppler)

MRI: Superior for posterior placentas and defining percreta anatomy. [3]

Management of PAS

Management of PAS requires multidisciplinary team (MDT) planning at a specialist center with: [3]

• Experienced pelvic surgeons (obstetrics, gynae-oncology, urology)
• Interventional radiology
• Blood bank with massive transfusion protocol
• Intensive care unit
• Neonatal intensive care unit

Delivery Timing:

• Elective caesarean at 35+0 to 36+6 weeks (earlier than uncomplicated praevia to reduce risk of labor/bleeding before planned delivery) [3]

Surgical Options:

1. Caesarean Hysterectomy (Gold Standard):

• Placenta left in situ
• Hysterectomy performed without attempting placental removal
• Reduces haemorrhage risk
• Definitive treatment

2. Conservative Management (Uterine Preservation):

• Indicated in women desiring future fertility
• Placenta left in situ
• Methotrexate sometimes used (controversial; not evidence-based)
• Requires weekly hCG + imaging follow-up
• Risk of delayed haemorrhage, infection, coagulopathy
• Success rate: 60–80% for accreta; lower for increta/percreta [3]

Perioperative Measures:

• Cell salvage
• Interventional radiology (prophylactic balloon occlusion of internal iliac arteries – controversial, not routinely recommended) [3]
• Cross-match 6–10 units packed red cells
• Activate massive transfusion protocol early

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9. Complications and Prognosis

Maternal Complications

Fetal and Neonatal Complications

Prognosis with Modern Care

With appropriate antenatal diagnosis, multidisciplinary planning, and delivery in a specialist center, maternal outcomes are excellent. [1,2]

Predictors of Good Outcome:

• Antenatal diagnosis on ultrasound
• Elective delivery in tertiary center
• Consultant-led surgery
• Blood products immediately available
• No emergency presentation with massive APH

Predictors of Poor Outcome:

• Emergency presentation with massive bleeding
• Undiagnosed PAS
• Delivery in non-specialist center
• Delayed resuscitation or surgical intervention

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10. Special Considerations

Anti-D Prophylaxis

All Rh-negative women with placenta praevia who experience vaginal bleeding require anti-D immunoglobulin to prevent alloimmunization. [1]

Protocol:

• Minimum dose: 500 IU IM within 72 hours of bleeding
• Kleihauer test to quantify fetomaternal haemorrhage (FMH)
• Additional anti-D if Kleihauer shows > 4mL fetal red cells
• Repeat anti-D every 6 weeks if ongoing bleeding or high-risk situation
• Standard postnatal anti-D after delivery

Vasa Praevia Association

Vasa praevia (fetal vessels crossing the internal os) occurs in approximately 1–2% of placenta praevia cases. [17] This is a critical association because:

• Rupture of membranes → immediate fetal exsanguination
• Fetal mortality 50–95% if undiagnosed [17]
• Diagnosis requires Color Doppler ultrasound at time of placental assessment

Management: Elective caesarean at 35–36 weeks before labor, with avoidance of membrane rupture.

Jehovah's Witness Patients

Women declining blood products present a unique challenge with placenta praevia. [1]

Enhanced Planning:

• Early MDT discussion with patient, haematology, anaesthetics
• Iron optimization (oral + IV)
• Erythropoietin (if acceptable to patient)
• Cell salvage (many Jehovah's Witnesses accept autologous blood)
• Consultant-led surgery
• Early recourse to uterine-sparing techniques (compression sutures, balloon tamponade)
• Immediate hysterectomy if uncontrolled bleeding (to prevent maternal death)

Twin Pregnancies

Placenta praevia in twins carries additional risks: [1]

• Higher incidence (OR 2.93)
• Larger placental mass → less likely to resolve with "migration"
• Greater risk of preterm labor
• Delivery timing: Individualize (35–37 weeks depending on chorionicity)

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11. Differential Diagnosis

Key Differentials for Third-Trimester Vaginal Bleeding

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12. Evidence-Based Guidelines

RCOG Green-top Guideline No. 27a (2018)

The Royal College of Obstetricians and Gynaecologists (RCOG) Green-top Guideline is the definitive UK evidence-based resource. [1]

Key Recommendations (Strength of Evidence):

Society for Maternal-Fetal Medicine (SMFM) / ACOG Consensus

The American College of Obstetricians and Gynecologists (ACOG) and SMFM published similar guidance. [2,18]

Key Points:

• Recommended delivery 36–37 weeks (aligns with RCOG)
• Emphasized importance of ultrasound screening for PAS in high-risk women
• Supported multidisciplinary team approach for PAS
• Advocated delivery in centers of excellence for PAS cases

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13. Examination Focus (Viva and OSCE)

Viva Scenarios

Scenario 1: 32-year-old G3P2 presents with painless vaginal bleeding at 30 weeks. She had two previous caesarean sections. How do you manage?

Model Answer: "This is antepartum haemorrhage in a high-risk patient. I would:

1. Resuscitate: ABC approach, large-bore IV access, FBC/G&S/cross-match, commence CTG
2. Avoid vaginal examination until placental position confirmed
3. Transvaginal ultrasound to determine placental location
4. If placenta praevia confirmed: Admit, give corticosteroids (betamethasone 12mg IM ×2), magnesium sulfate for neuroprotection less than 30 weeks, and anti-D if Rh-negative
5. Screen for placenta accreta spectrum given 2 prior CS – look for lacunae, loss of clear zone, bladder involvement
6. Observe for 48h; if bleeding settles, plan elective caesarean at 36–37 weeks in tertiary center with MDT planning (senior surgeon, anaesthetist, blood products, possible hysterectomy consent)"

Scenario 2: A 20-week anomaly scan shows a placenta praevia. The patient is anxious. What do you tell her?

Model Answer: "I would reassure her that 90% of low-lying placentas at 20 weeks resolve by 36 weeks through a process called placental migration. We will arrange a follow-up scan at 32 weeks. If it has resolved, she can plan for normal delivery. If it persists, we will rescan at 36 weeks and plan accordingly. In the meantime, she should avoid intercourse (pelvic rest) and come to hospital immediately if she experiences any vaginal bleeding. The key message is: most cases resolve, and we will closely monitor her."

Scenario 3: At caesarean section for placenta praevia, the placenta does not separate and there is torrential bleeding. What do you do?

Model Answer: "This suggests placenta accreta. I would:

1. Call for help: Senior obstetrician, senior anaesthetist, haematology (massive transfusion protocol)
2. Do not forcibly remove placenta – this worsens bleeding
3. Resuscitate: IV crystalloid, activate massive transfusion, correct coagulopathy
4. Immediate options: Bimanual compression, uterotonics (oxytocin, carboprost, misoprostol), Bakri balloon, compression sutures (B-Lynch)
5. Definitive: Caesarean hysterectomy – this is life-saving and should not be delayed if bleeding is uncontrolled
6. Consent discussion (ideally pre-operatively) should have covered this risk"

OSCE Stations

Station: Counsel a Woman with Placenta Praevia Diagnosed at 32 Weeks

Candidate Task:

• Explain the diagnosis
• Discuss delivery plan
• Address risks and safety netting

Key Points to Cover:

• "Your placenta is low-lying and covering the birth canal. This means you will need a caesarean section."
• "We will plan this for around 36–37 weeks, a bit earlier than normal, to avoid going into labor naturally, which could cause heavy bleeding."
• "Before then, avoid intercourse and come to hospital immediately if you have bleeding, pain, or contractions."
• "If you bleed heavily before the planned date, we may need to deliver your baby earlier as an emergency."
• "The operation will be done by senior doctors with blood available. There is a small risk you may need a hysterectomy if bleeding cannot be controlled, especially if the placenta is deeply stuck."
• "Your baby will go to the neonatal unit briefly for checks because of being born a bit early, but outcomes are generally very good."

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14. Patient Explanation (Layperson Level)

What is Placenta Praevia?

"The placenta is the organ that feeds your baby inside the womb. Normally, it attaches to the top or side of the womb. In your case, the placenta has attached very low down and is covering the 'exit' (the cervix) where the baby needs to come out during birth."

Why is it a Problem?

"Because the placenta is blocking the way out, your baby cannot be born through the vagina. As your womb prepares for birth, the lower part stretches, which can cause the placenta to start peeling away. This leads to bleeding – and it can sometimes be heavy. The bleeding is painless, which is different from other pregnancy complications."

What Will Happen?

"We will monitor you closely with ultrasound scans. Many low-lying placentas 'move up' as the womb grows, so this might resolve on its own. If it doesn't, you will need a caesarean section (an operation to deliver your baby through a cut in your tummy)."

When Will the Baby Be Delivered?

"We usually plan the caesarean for around 37 weeks (a bit earlier than the normal 40 weeks). This is because we want to deliver the baby before you go into labor naturally, which could cause dangerous bleeding."

What If I Start Bleeding Before Then?

"If you have any bleeding, come to the hospital immediately. Even a small amount of bleeding can be a warning sign. If the bleeding is heavy, we may need to deliver your baby earlier, even if that means the baby is premature."

Are There Other Risks?

"If you have had a caesarean section before, there is a risk that the placenta has grown too deeply into the scar. This is called placenta accreta. If that happens, the placenta may not come away easily after delivery, and we might need to remove your womb to stop the bleeding. We will discuss this with you before the operation."

What Can I Do to Stay Safe?

• Avoid sex (pelvic rest)
• Come to hospital immediately if you have bleeding
• Attend all your scans so we can plan carefully

"The good news is that with modern care, the vast majority of women with placenta praevia have safe deliveries and healthy babies."

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15. Key Clinical Pearls for Examinations

1. NO digital vaginal examination in any woman with vaginal bleeding until placental position is confirmed by ultrasound.

2. Painless bleeding is the hallmark – this differentiates praevia from abruption.

3. Transvaginal ultrasound is SAFE and more accurate than transabdominal scanning.

4. 90% of second-trimester low-lying placentas resolve – reassure anxious patients at 20-week scan.

5. Placenta praevia + previous CS = screen for accreta – do not miss this!

6. Delivery timing: 36–37 weeks (asymptomatic); 35–36 weeks (PAS).

7. Regional anaesthesia is preferred over general anaesthesia for elective caesarean.

8. Massive haemorrhage risk: Cross-match blood, have senior surgeons, consent for hysterectomy.

9. Anti-D for all Rh-negative women after any bleeding episode.

10. Sentinel bleed: A small bleed often precedes a major haemorrhage – admit and observe.

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16. Red Flag Features Requiring Immediate Action

┌─────────────────────────────────────────────────────────────────────────────┐
│                              RED FLAGS                                      │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│  ⚠️  MASSIVE PAINLESS VAGINAL BLEEDING                                      │
│      → Call obstetric emergency team, activate Code Red                     │
│      → IV resuscitation, cross-match, prepare for immediate CS              │
│                                                                             │
│  ⚠️  HEMODYNAMIC INSTABILITY (HR > 110, BP less than 90 systolic)                     │
│      → Activate massive transfusion protocol                                │
│      → Senior anaesthetist involvement                                      │
│                                                                             │
│  ⚠️  FETAL BRADYCARDIA / PATHOLOGICAL CTG                                   │
│      → Consider vasa praevia or abruption                                   │
│      → Prepare for Category 1 caesarean section                             │
│                                                                             │
│  ⚠️  SUSPECTED PLACENTA ACCRETA SPECTRUM                                    │
│      → Do NOT attempt forcible placental removal                            │
│      → Multidisciplinary team (urology, interventional radiology)           │
│      → Consent for possible hysterectomy                                    │
│                                                                             │
│  ⚠️  PLACENTA PRAEVIA + LABOR ONSET BEFORE PLANNED DELIVERY                 │
│      → Immediate caesarean section (do not allow vaginal delivery)          │
│      → Risk of catastrophic haemorrhage if cervix dilates                   │
│                                                                             │
└─────────────────────────────────────────────────────────────────────────────┘

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17. Future Pregnancies and Contraception

Women with a history of placenta praevia have a 4–8% recurrence risk in subsequent pregnancies. [1]

Preconception Counselling

• Optimize iron stores and anaemia treatment
• Plan pregnancy at tertiary center if multiple previous CS or previous PAS
• Early ultrasound in next pregnancy (10–12 weeks) to assess placental location

Contraception After Delivery

Following delivery complicated by placenta praevia (especially with caesarean section):

• Long-acting reversible contraception (LARC) recommended if family complete
• Intrauterine device (Mirena/copper coil) – can be inserted at caesarean section or 6 weeks postpartum
• Avoid estrogen-containing contraception for first 6 weeks (VTE risk)

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18. Audit and Quality Indicators

Clinical Audit Standards (RCOG)

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19. Summary Algorithm

┌─────────────────────────────────────────────────────────────────────────────┐
│                  PLACENTA PRAEVIA MANAGEMENT SUMMARY                        │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                             │
│  DIAGNOSIS (Transvaginal Ultrasound)                                        │
│  • Low-lying placenta (less than 20mm from os) or covering os                        │
│                          ↓                                                  │
│  CLASSIFICATION                                                             │
│  • Placenta praevia (covering os) → Caesarean mandatory                     │
│  • Low-lying (edge less than 20mm, not covering) → Rescan 36w, individualize         │
│                          ↓                                                  │
│  RISK STRATIFICATION                                                        │
│  • Prior CS? → Screen for PAS (ultrasound ± MRI)                            │
│  • Multiple risk factors? → Plan tertiary center delivery                   │
│                          ↓                                                  │
│  ANTENATAL MANAGEMENT                                                       │
│  • Asymptomatic → Outpatient (if appropriate) with safety netting           │
│  • Bleeding episode → Admit, stabilize, corticosteroids, observe            │
│  • Optimize Hb, pelvic rest, anti-D if Rh negative                          │
│                          ↓                                                  │
│  DELIVERY PLANNING                                                          │
│  • Timing: 36-37 weeks (praevia); 35-36 weeks (PAS)                         │
│  • Consultant-led caesarean section                                         │
│  • Cross-match blood, cell salvage, senior anaesthetist                     │
│  • Consent: Risk of PPH, hysterectomy, blood transfusion                    │
│                          ↓                                                  │
│  EMERGENCY MANAGEMENT (if massive APH)                                      │
│  • Resuscitate: IV access, crystalloid, activate massive transfusion        │
│  • Emergency Category 1 caesarean section                                   │
│  • Senior surgeons, interventional radiology if available                   │
│  • Hysterectomy if uncontrolled bleeding                                    │
│                                                                             │
└─────────────────────────────────────────────────────────────────────────────┘

---

20. References

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2. Jain V, Bos H, Bujold E. Guideline No. 402: Diagnosis and Management of Placenta Previa. J Obstet Gynaecol Can. 2020;42(7):906-917.e1. doi:10.1016/j.jogc.2019.07.019

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14. Fratelli N, Prefumo F, Maggi C, et al. Third-trimester ultrasound for antenatal diagnosis of placenta accreta spectrum in women with placenta previa: results from the ADoPAD study. Ultrasound Obstet Gynecol. 2022;60(3):381-389. doi:10.1002/uog.24889

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16. Society of Gynecologic Oncology, American College of Obstetricians and Gynecologists, Society for Maternal–Fetal Medicine. Placenta Accreta Spectrum. Am J Obstet Gynecol. 2018;219(6):B2-B16. doi:10.1016/j.ajog.2018.09.042

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