Placenta Previa

Aka: Placenta Previa

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II. Epidemiology

  1. Incidence
    1. Most common cause of Third Trimester Bleeding
    2. Second trimester (16-20 weeks): 5%
    3. Term: 0.5% (90% of low placentas resolve by term)

III. Definition

  1. Low Implantation of placenta within 2 cm of internal os
  2. Placenta lies alongside or in front of presenting part

IV. Types

  1. Type 1: Low Implantation
    1. Lower placenta margin dips into lower uterine segment
    2. Edge lies within 2 to 3.5 cm of internal cervical os
  2. Type 2: Marginal Placenta
    1. Placenta within 2 cm of internal os, does not cover
  3. Type 3: Partial Previa
    1. Placenta covers internal os when closed
    2. Placenta does not cover os when fully dilated
  4. Type 4: Complete Previa (Central Previa)
    1. Placenta covers internal os even when fully dilated

V. Pathophysiology

  1. Placenta usually implants at fundus
    1. Fundal blood supply is better than lower Uterus
  2. Abnormal implantat occurs at uterine scar or disruption

VI. Risk factors

  1. Previous Cesarean Section or uterine curettage
    1. Associated with placenta accreta
  2. High Parity or Multiple Gestations
  3. Older maternal age
  4. Chronic Hypertension
  5. Multiple Gestation
  6. Tobacco Abuse
  7. Preterm Labor
  8. Previous uterine instrumentation

VII. Associated Conditions

  1. Abnormal presentation (placenta raises presenting part)
    1. Oblique Lie
    2. Transverse Lie
  2. Placental Abruption
  3. Intrauterine Growth Retardation
  4. Placenta accreta (especially if prior ceserean section)
  5. Antepartum bleeding
  6. Postpartum Hemorrhage
  7. Preterm delivery

VIII. Symptoms

  1. Painless uterine bleeding after 18-20 weeks gestation
    1. Typically occurs at 27-32 weeks: "Sentinel bleed"
    2. May be provoked with intercourse, contractions
  2. Abdomen soft and non-tender

IX. Exam

  1. Avoid digital vaginal exam or speculum exam if suspected Placenta Previa

X. Labs

  1. See Late Pregnancy Bleeding
  2. Complete Blood Count
  3. Blood Type and Screen
    1. Type and cross match for 2-4 units
  4. Coagulation studies (PT/INR, PTT)
  5. Fibrinogen
    1. Fibrinogen <300 mg/dl may suggest DIC
  6. Kleihauer-Betke Test
  7. Preterm Labor Management
    1. Consider Corticosteroids
    2. Consider Magnesium Sulfate

XI. Differential Diagnosis

  1. Late Pregnancy Bleeding

XII. Imaging: Serial obstetric Transvaginal Ultrasound

  1. Transvaginal Ultrasound is safe and preferred option
    1. Transabdominal Ultrasound lacks adequate precision
    2. Transvaginal changes diagnosis in one in four cases
  2. General evaluation
    1. Interval Fetal Growth
    2. Evaluate for resolution or partial previa
      1. Overlap <1.5 cm over os at 20 wks: Usually resolves
      2. Overlap >2.5 cm over os at 20 wks: Usually persists
      3. Placenta is unlikely to clear cervical os at term if bulk of placenta is over the os at 24 weeks or later
      4. References
        1. Taipale (1998) Ultrasound Obstet Gynecol 12:422-5 [PubMed]
    3. Evaluate for placenta acreta if prior ceserean
  3. Visualization aids
    1. Anterior Placenta Previa
      1. View placental edge with full, then empty Bladder
    2. Posterior Placenta Previa
      1. Transducer lateral and angled toward midline
      2. Consider slight trendelenberg position
      3. Consider gentle Transvaginal Ultrasound
        1. Insert probe only partially into vagina

XIII. Management: Counseling

  1. Risk of severe life-threatening Hemorrhage
    1. Risk of fetal death
    2. Risk of maternal death
  2. Blood Transfusion may be necessary
  3. Hysterectomy may be needed to control bleeding

XIV. Management: Protocol

  1. Late Pregnancy Bleeding
    1. Ceserean delivery indications
      1. 37 weeks or
      2. Unstable
        1. Heavy uterine bleeding
        2. Hypotension
        3. Fetal Distress (e.g. non-reassuring fetal tracing)
    2. Observation protocol
      1. Hospital observation
        1. Limited bleeding that has resolved at <24 weeks gestation may have close interval follow-up
      2. Follow serial Hemoglobins
      3. Type and cross in preparation for transfusion
      4. Administer Corticosteroids if gestation <34 weeks
        1. See Preterm Labor Management
  2. No bleeding
    1. Ceserean delivery after 36 weeks
      1. Assess for Fetal Lung Maturity with Amniocentesis
    2. Pelvic rest until 36 weeks
    3. Cervical cerclage may be considered
      1. Cobo (1998) Am J Obstet Gynecol 179:122-5 [PubMed]
    4. Follow serial Transvaginal Ultrasounds
      1. Ultrasound at 28-30 weeks
      2. Ultrasound at 36 weeks

XV. Management: General

  1. See also Late Pregnancy Bleeding
  2. Pelvic rest
    1. No sexual intercourse
    2. Avoid digital cervical exam
    3. Gentle speculum exam is permitted (insert 90 degrees)
  3. Cesarean Section at tertiary care center recommended
    1. Delay delivery until mature lung studies if possible
    2. Tocolysis with Magnesium Sulfate is safe
    3. Regional (spinal) Anesthesia preferred over general
      1. General Anesthesia may increase bleeding risk
    4. Marginal previa may allow Vaginal Delivery
      1. Evaluation by experienced clinician only
      2. Double set-up is mandatory for vaginal exam
      3. NSVD indications
        1. Head engaged: Can tamponade marginal previa and
        2. No brisk bleeding on exam and
        3. Close monitoring and
        4. In-house OR team for stat Ceserean
  4. Bleeding management
    1. See Late Pregnancy Bleeding
    2. Placenta Previa with active bleeding is an emergency
      1. See Hemorrhagic Shock
      2. Fluid Resuscitation and Blood Transfusion as needed
      3. Emergent obstetric Consultation
      4. Intensive monitoring of Vital Signs including Blood Pressure
      5. Urine catheter for Urine Output monitoring
      6. Quantify blood loss

XVI. References

  1. Bavolek and Mason in Herbert (2018) EM:Rap 18(10): 15-6
  2. Lall (2017) Crit Dec Emerg Med 31(1): 3-9
  3. Bhide (2004) Curr Opin Obstet Gynecol 16:447-51 [PubMed]
  4. Sakornbut (2007) Am Fam Physician 75:1199-206 [PubMed]

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