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Snapshot
  • A 29-year-old G2P1 female presents to labor and delivery triage with bleeding in the third trimester. Her first pregnancy was a cesarean delivery delivered at 37 weeks. She describes her bleeding as painless spotting without abdominal pain. An urgent transabdominal ultrasound is performed, showing a viable fetus and normal amniotic fluid. A transvaginal ultrasound is subsequently performed, and shows the placental edge located 1cm from the internal cervical os.
Introduction
 placenta previa
  • 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
  • Epidemiology
    • incidence
      • occurs in approximately 1 per 250 births
    • risk factors
      • previous placenta previa
      • previous cesarean delivery
      • multiple gestations
  • Associated conditions
    • placenta previa-accreta spectrum
      • placenta previa is present along with placenta accreta, placenta increta, or placenta percreta
Presentation
  • Most common presentation is asymptomatic finding on routine ultrasound at 16-20 weeks of gestation
  • Symptoms  
    • 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
  • Ultrasonography
    • 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
  • 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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