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Antepartum Hemorrhage (APH), Placenta Previa, and Placenta Accreta Spectrum (PAS): A Comprehensive PG-Level Discussion

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PART I: ANTEPARTUM HEMORRHAGE (APH)

Definition and Epidemiology

Differential Diagnosis of APH

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PART II: PLACENTA PREVIA

Definition and Classification

Important terminology update: The previous categories of complete, partial, and marginal placenta previa are no longer recommended. Current NICHD/SMFM consensus terminology uses:

• "Placenta previa" = placenta covering the internal os
• "Low-lying placenta" = placental edge within 2 cm but not covering the os
• "Normal" = placental edge >20 mm from the internal os
• Creasy & Resnik; Key Points section

Incidence

• Placenta previa affects approximately 0.5% of all third-trimester pregnancies (1 in 200-250 pregnancies)
• It is diagnosed in 10% of mid-trimester sonograms, but the vast majority resolve due to placental migration (trophotropism)
• At least 90% of placentas identified as low-lying or previa in early pregnancy ultimately resolve by the third trimester
• Creasy & Resnik; Textbook of Family Medicine 9e

Pathogenesis - "Placental Migration"

1. The placenta grows toward better blood supply at the uterine fundus (trophotropism)
2. The distal portions closer to the lower segment with poor blood supply undergo regression and atrophy
3. Differential growth of the lower uterine segment with advancing gestation further increases the distance between the placental edge and the cervix

Risk Factors

Clinical Features

• Classic presentation: Painless, bright-red vaginal bleeding, usually after the 28th week (7th month). The painless nature distinguishes it from abruption.
• Several small "herald bleeds" may precede a major hemorrhage
• In up to 10% of cases, there is no bleeding until onset of labor
• Abnormal fetal lie (transverse, oblique) is common because the previa occupies the lower pole of the uterus, preventing head engagement

Diagnosis

• If placental edge is >20 mm from the internal os → report as "normal"
• If placental edge is within 20 mm but not covering the os → report as "low-lying"
• Placenta covering the internal os → "placenta previa"
• TVUS has high sensitivity and specificity; transabdominal scanning frequently overestimates proximity due to bladder distension and posterior placentas

Associated Conditions

• Placenta accreta spectrum (critically important - see Part III)
• Vasa previa
• Fetal malpresentation
• Preterm birth
• Intrauterine growth restriction (IUGR)

Management of Placenta Previa

Antepartum (Expectant) Management

• Inpatient vs outpatient: Evidence suggests outpatient management is reasonable in selected stable patients without active bleeding. Inpatient admission is indicated for active bleeding, contractions, or remote location.
• Pelvic rest (no intercourse, no vaginal examinations)
• Avoidance of strenuous activity
• IV access and crossmatched blood should be available
• Tocolysis may be used with caution for preterm uterine contractions to prolong gestation (tocolysis is generally considered safe in the context of placenta previa, though evidence is limited)
• Antenatal corticosteroids if preterm delivery anticipated before 34 weeks
• Serial ultrasound surveillance

Timing of Delivery

• Uncomplicated placenta previa: deliver at 36-37 weeks (planned cesarean section)
• With placenta accreta: earlier delivery, typically 34-37 weeks (see below)
• Amniocentesis for fetal lung maturity imposes unnecessary delay and is NOT recommended in current practice - Creasy & Resnik

Mode of Delivery

• Neuraxial anesthesia is preferred (lower blood loss, less need for transfusion compared to general anesthesia)
• General anesthesia is reserved for hemodynamic instability or patient refusal
• Both uterine atony and placenta accreta can cause massive postpartum hemorrhage in these cases

Management of Acute Hemorrhage from Placenta Previa

1. Stabilize the patient: IV access x2, full blood count, coagulation screen, crossmatch
2. Ultrasound to confirm diagnosis and fetal wellbeing
3. If hemorrhage is life-threatening or fetus is mature: emergency cesarean section
4. Blood transfusion and massive hemorrhage protocol if needed
5. Uterotonic agents, balloon tamponade, B-Lynch suture, uterine artery ligation, or hysterectomy for refractory bleeding

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PART III: PLACENTA ACCRETA SPECTRUM (PAS)

Terminology and Classification

Pathophysiology

Incidence and Trends

• Incidence is rising sharply due to the global rise in cesarean section rates
• Current estimates: 1 in 300-500 pregnancies in recent cohorts
• Historical incidence (1970s): 1 in 30,000
• Current incidence (population-based): approximately 3 per 1,000 deliveries
• Creasy & Resnik; Rosen's Emergency Medicine

Risk Factors - The Critical Synergy of Previa + Prior CS

Ultrasound Diagnosis of PAS

• Color flow Doppler shows turbulent flow in lacunar spaces and increased vascularity at the placenta-uterus interface
• First-trimester diagnosis is possible and is particularly accurate in cases of cesarean scar ectopic pregnancy
• All women with clinical risk factors should be referred to a unit with appropriate expertise in PAS diagnosis

Role of MRI in PAS

• No adverse outcome has been found from MRI without gadolinium during pregnancy
• Creasy & Resnik

Antenatal Surveillance and Multidisciplinary Care

Timing of Delivery in PAS

• Planned delivery at 34-35 weeks (Creasy & Resnik recommendation) after antenatal corticosteroids for fetal lung maturity
• Decision analysis supports 34-37 weeks without amniocentesis for lung maturity
• Earlier delivery in cases with cervical involvement or suspected percreta
• Emergency delivery if life-threatening hemorrhage

Surgical Management of PAS

Standard Approach: Cesarean Hysterectomy

1. Fundal uterine incision - to avoid cutting through placenta and triggering hemorrhage before clamping the cord
2. Cord is clamped after delivery of the baby
3. Placenta is left in situ (do not attempt manual removal, which will precipitate massive hemorrhage)
4. Proceed to total abdominal hysterectomy with the placenta still in place
5. Complex dissection of lower uterine segment and parametrial areas may be required
6. Pelvic surgeon capable of wide resection should be part of the team

Conservative Management (Uterus-Sparing Approaches)

• Conservative management: less estimated blood loss (WMD -1624 mL), fewer units of packed RBCs (WMD -2.37 units), shorter operating time (WMD -74 min)
• Lower risks of bladder injury (RR 0.24), ICU admission (RR 0.24), coagulopathy (RR 0.20)
• BUT increased risk of endometritis (RR 10.91) and readmission (RR 8.99)
• 25% ultimately required hysterectomy (primary or delayed)
• UAE was used in 78% of conservatively managed cases
• Conclusion: Conservative management is an effective alternative when fertility preservation is desired, with informed consent about limitations

• Cesarean hysterectomy associated with significantly higher blood loss vs. placenta in situ (mean difference +974 mL) and vs. local resection (+740 mL)
• Higher risk of genitourinary injury with hysterectomy (OR 3.79 vs. placenta in situ; OR 4.11 vs. local resection)
• Higher ICU admission with hysterectomy vs. placenta in situ (OR 7.98)
• No difference in GI injury or thromboembolic events
• Conclusion: Conservative management associated with reduced surgical morbidity

• Majority (69.4%) treated with myometrial resection and repair
• Overall hysterectomy rate when conservative surgery was attempted: 11.2%
• Urologic complication rate: 8.8%
• Mean blood loss: ~1,800 mL in both myometrial resection and other conservative approaches
• Conclusion: Uterine-sparing surgery feasible in high percentage of PAS patients with outcomes comparable to hysterectomy

Adjunctive Hemostatic Techniques

• Balloon occlusion of internal iliac or aortic vessels: Preoperative placement of balloon-tipped catheters via femoral artery approach under fluoroscopy. Benefit remains controversial - published studies show no proven benefit and reports of embolic complications. The utility is unclear due to variable timing of deployment. A comprehensive literature review concluded larger studies are needed.
• Cell salvage (intraoperative autologous blood collection)
• Uterine artery embolization (UAE): Used extensively as an adjunct in conservative management
• Massive transfusion protocol activation: Should be planned preoperatively

Urological Complications - Updated Evidence

• Overall urological complications in PAS surgery: 15.2%
• Cystotomy (total): 13.5% (intentional 7.7%, unintentional 7.2%)
• By severity: accreta/increta: 9.4%; percreta: 38.5%
• By approach: hysterectomy 19.4%; conservative surgery 12.2%
• Emergency vs. planned: 24.6% vs. 15.4%
• Key message: Urological morbidity is high, especially for percreta and emergency cases. Standardized PAS diagnosis protocols are needed.

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PART IV: ABRUPTIO PLACENTAE (for completeness in APH discussion)

Definition

Epidemiology

• Clinically recognized abruption: approximately 1% of all pregnancies
• Abruption causing fetal death: 1 in every 420 deliveries
• If placentas are routinely examined postdelivery, pathological evidence of abruption may be found in up to 4% of cases (most subclinical)
• Incidence has increased by approximately 25% in the USA over recent decades, with a disproportionate increase in Black women
• Incidence peaks at 24-26 weeks' gestation
• Approximately 10% of all preterm births are secondary to abruption
• Perinatal mortality ranges from 9-12% in developed countries; maternal mortality <1%
• Creasy & Resnik

Pathogenesis

• Low PAPP-A levels (placenta with impaired function)
• Poor trophoblastic invasion
• Abnormal uterine artery Doppler (inadequate remodeling of maternal arterioles)
• Strong association with preeclampsia, IUGR, and abruption (all sharing a common placental pathology pathway)

• Fetal hypoxia → fetal death (>50% separation → likely fetal death)
• Activation of coagulation cascade → DIC
• Hemorrhagic shock → worsening DIC → downward spiral
• Bleeding into myometrium → Couvelaire uterus (atonic, woody-hard) → increases risk of postpartum hemorrhage

Types

• 10% of abruptions are concealed - external bleeding is an unreliable guide to severity

Risk Factors for Abruption

• Chronic hypertension and preeclampsia (most important)
• Previous abruption (recurrence risk up to 20-fold increased)
• Cigarette smoking
• Cocaine and other vasoactive drug use
• Trauma (motor vehicle accidents, domestic violence)
• Multiple gestation
• Preterm premature rupture of membranes (pPROM)
• Thrombophilias and hyperhomocysteinemia
• Low PAPP-A (<5th percentile) on first-trimester screening
• Elevated second-trimester AFP (>2 MoM)
• Elevated second-trimester hCG (>3 MoM)
• Creasy & Resnik

Clinical Features

1. Vaginal bleeding (dark, clotted blood - contrast with the bright-red painless bleeding of previa)
2. Abdominal/uterine pain and tenderness (the key differentiator from previa)
3. Uterine hypertonicity

• Uterine contractions (may precipitate preterm labor)
• Fetal compromise/distress on CTG
• With posterior abruption: severe back pain as the only symptom
• Massive concealed abruption: severe pain, hard "board-like" tonically contracting uterus, fetal death - classically associated with severe preeclampsia or cocaine use
• Coagulopathy (DIC) in severe cases

Diagnosis

• Fresh clot may be isoechoic to placenta
• Retroplacental hematoma is visible in only about 25% of cases on ultrasound
• A negative ultrasound does NOT rule out abruption
• Creasy & Resnik; Key Points: "Abruption remains a clinical diagnosis - imaging is useful only to exclude placenta previa"

• Full blood count, coagulation profile (PT, APTT, fibrinogen - fibrinogen <200 mg/dL suggests severe abruption, <150 mg/dL indicates DIC)
• Kleihauer-Betke test in Rh-negative women to quantify fetomaternal hemorrhage
• Continuous CTG
• Renal function (acute tubular necrosis from prolonged hypoperfusion)

Management of Abruption

• Expectant management with close inpatient observation
• Serial ultrasound and fetal monitoring
• Antenatal corticosteroids if <34 weeks

• Artificial rupture of membranes (stabilizes fetal presenting part against placenta, reduces pressure)
• Oxytocin augmentation if in labor
• Continuous fetal monitoring
• Urgent CS if non-reassuring fetal status

• Emergency cesarean section if fetus is alive
• If fetal death has occurred and mother is stable: vaginal delivery may be attempted (avoids CS in setting of DIC)
• Aggressive resuscitation, massive transfusion protocol
• Coagulation replacement (FFP, cryoprecipitate, platelets)
• Manage Couvelaire uterus: uterotonics, B-Lynch, hysterectomy if necessary

• Modify risk factors: treat hypertension, smoking cessation, substance abuse cessation
• Folate supplementation for proven hyperhomocysteinemia
• Creasy & Resnik

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PART V: CLINICALLY IMPORTANT INTERRELATIONSHIPS

The APH-Previa-PAS Triangle

1. Placenta previa is the principal risk factor for PAS (co-occurrence >60% with 3+ prior CS)
2. PAS is the most common cause of emergency peripartum hysterectomy
3. APH in a patient with previa should always prompt evaluation for PAS before any surgical intervention
4. Low-lying placenta that resolves clinically still carries elevated PPH risk: 8% PPH rate even when resolved, and PAS affects 9% of all low-lying placenta cases - Bonanni et al. 2025
5. All women with prior cesarean sections and current placenta previa must be evaluated for PAS - Creasy & Resnik Key Points

Key Points Summary (Examination-Level)

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Recent Literature Updates (2023-2026) Summary

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• Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice, 8e - Chapters 27 (Abnormal Placentation - Imaging) and 43 (Placenta Previa, Placenta Accreta, Abruptio Placentae, Vasa Previa)
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9e - Chapter on Antepartum Hemorrhage
• Morgan & Mikhail's Clinical Anesthesiology, 7e - Obstetric Anesthesia chapter
• Textbook of Family Medicine, 9e
• Rosen's Emergency Medicine: Concepts and Clinical Practice
• Miller's Anesthesia, 10e - Obstetric Anesthesia