Placenta Previa

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

• 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