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Updated: Sep 27 2022

Placenta Previa

  • Snapshot
    • A 33-year-old G4P3 presents to the obstetrician at 29 weeks gestation with painless vaginal bleeding. The bleeding began 2 hours ago and she has delivered a substantial amount of blood with clots. She is having no uterine contractions and the fetal pulse is 150/min. Her last pregnancy was delivered by emergency cesarean at 37 weeks due to double-footing breech presentation during labor. Findings on transvaginal ultrasound show the placenta extending over the internal cervical os.
  • Epidemiology
    • Incidence
      • occurs in approximately 1 per 250 births
      • location
        • most common tricuspid valve
    • Risk factors
      • previous placenta previa
      • previous cesarean delivery
      • multiple gestations
  • Etiology
    • Overview
      • placenta previa is a condition characterized placental tissue extending over or < 2 cm from the internal cervical os and is associated with painless third trimester bleeding
    • Associated conditions
      • placenta previa-accreta spectrum
        • placenta previa is present along with placenta accreta, placenta increta, or placenta percreta
  • Presentation
    • Symptoms
      • asymptomatic finding on routine ultrasound
      • painless vaginal bleeding
        • up to 90% of cases
      • uterine contractions, pain, and bleeding
        • 10-20% of cases
    • Physical exam
      • digital vaginal examination is contraindicated until placenta previa is excluded (may result in severe hemorrhage)
      • findings may include the following
        • hemorrhage
          • usually spontaneously ceases after 1-2 hours
        • hypotension
        • tachycardia
        • usually no fetal distress (in contrast with vasa previa)
  • Imaging
    • Ultrasound
      • transvaginal ultrasound
        • gold standard for diagnosis of placenta previa
        • identification of placental tissue extending over the internal cervical os on 2nd or 3rd trimester imaging
      • transabdominal ultrasound
        • can be used as a screening test or in conjunction with transvaginal ultrasound
          • if distance between edge of placenta and cervical os is ≤ 2 cm on transabdominal ultrasound, perform transvaginal ultrasound to better visualize placental position
  • Studies
    • Serum labs
      • Rh compatability test
      • Complete blood cell (CBC) count
      • Prothrombin time (PT) and activated partial thromboplastin time (aPTT)
      • Blood type and cross
      • Levels of fibrin split products (FSP) and fibrinogen
  • Differential
    • Abruptio placentae
      • key distinguishing factors
        • placenta prematurely separates from the uterine wall
        • presents with painful bleeding that does not spontaneously cease
    • Placenta accreta
      • key distinguishing factors
        • placenta invades the uterine wall
        • placenta does not separate after delivery, which may lead to postpartum bleeding
    • Vasa previa
      • key distinguishing factors
        • fetal vessels extend over the internal cervical os
        • presents with fetal heart decelerations due to compression of umbilical vessels
  • Treatment
    • Medical
      • monitoring
        • in the case of asymptomatic placenta previa
          • monitor placental position
          • determine whether placenta accreta is also present
          • if persistent placenta previa, plan for cesarean delivery
      • hemostasis
        • in the case of actively bleeding placenta previa
          • admit for maternal and fetal monitoring
          • achieve and maintain maternal hemodynamic stability
    • Surgical
      • cesarean delivery
        • cesarean delivery should be performed in these cases:
          • active labor
          • fetal distress (category III fetal heart rate tracing that does not respond to in utero resuscitation)
          • inability to achieve maternal hemodynamic stability
          • significant vaginal bleeding after 34 weeks of gestation
  • Complications
    • Congenital malformations
      • associated with 2-fold increase
    • Fetal malpresentation
    • Vasa previa
      • rupture of fetal vessels that cross the membranes covering the cervix
      • cesarean delivery indicated
    • Postpartum hemorrhage
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