Placenta Previa – Nomenclature, Diagnosis and Clinical Management

Clinical Actions:

The incidence of placenta previa is 1/200 pregnancies. Most cases of placenta previa will be identified prenatally by prenatal ultrasound. The following is recommended regarding mode and timing of delivery

  • Placenta previa: Cesarean delivery only
  • Placenta edge is ≥2.0 cm from the internal cervical os
    • Trial of labor is appropriate
  • Placental edge is between 1.0 cm and 2.0 cm from the internal cervical os
    • Management is uncertain
  • Timing of delivery in stable cases
    • ACOG/SMFM: 36w0d to 37w6d
  • Hospitalize when there are contractions or vaginal bleeding
  • Consider corticosteroids to enhance pulmonary maturity when there is vaginal bleeding <34 weeks gestation
  • The benefits of tocolysis, bed rest, pelvic rest and reduced activity is uncertain

Synopsis:

The nomenclature has been modified and the terms partial and marginal have been eliminated. All placentas which overlie or abut the internal cervical os (to any degree) should be referred to as placenta previa. A placenta which is near to but not overlying the os is termed a low-lying placenta.

Key points:

  • Role of ultrasound
    • Transvaginal ultrasound is the recommended approach
    • Transvaginal ultrasound is more accurate than transabdominal approach
    • If placenta previa is suspected on transabdominal ultrasound, a transvaginal ultrasound should be performed
  • Placenta previa identified during second trimester ultrasound
    • Placenta previa may be seen in 1 to 4% of second trimester ultrasound exams
    • 10 to 20% of previas diagnosed at 20 weeks gestation will remain a previa in the late 3rd trimester
    • Repeat ultrasound at 32 weeks gestation
  • The incidence of placenta previa is increased by
    • Number of previous cesarean sections
    • Number of previous spontaneous deliveries
    • the number of elective terminations
    • prior uterine surgery
    • maternal parity
    • maternal age
    • smoking
    • cocaine use
    • multiple gestations
    • prior placenta previa
  • Fetal complications are primarily those associated with prematurity
  • There is an increased risk of postpartum hemorrhage in patient with placenta previa
  • General anesthesia may increase blood loss without improving safety


Learn More – Primary Sources:

Abnormal Placentation: Placenta Previa, Vasa Previa, and Placenta Accreta

Society for Maternal-Fetal Medicine (SMFM) Consult Series #44: management of bleeding in the late preterm period

The Incidence of Postpartum Hemorrhage in Pregnant Women with Placenta Previa: A Systematic Review and Meta-Analysis

Analysis of first and second trimester maternal serum analytes for the prediction of morbidly adherent placenta requiring hysterectomy