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Placenta Previa

Placenta Previa is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

  • Complete/total previa: Placenta covers the entire os.
  • Partial previa: Placenta covers part of internal cervical os.
  • Marginal previa: Placental edge is adjacent to cervical os by ultrasound (US), but not overlapping, usually within 2 cm of os.
  • Low-lying placenta: placental edge located in the lower uterine segment but does not encroach on/cover the os; has been defined as within 2 to 3 cm of cervical os by US

Epidemiology

  • Most common cause of painless vaginal bleeding in the 2nd and 3rd trimester
  • 10% of low-lying placentas at 10 to 20 weeks persist to term.

Incidence
  • 1–6% of pregnancies have sonographic evidence of previa between 10 to 20 weeks’ of gestation.
  • Recurrence rate of 4–8% with prior placenta previa
  • Approximately 80% of women with placenta previa in the 2nd trimester will have resolution by term.
  • Persistent placenta previa complicate 1 in 200 pregnancies.
  • Extension over the cervical os is the best predictor of placenta previa at time of delivery.
  • The earlier the previa is detected, the less change it will persist at the time of delivery.
  • Increased incidence parallels the increasing rate of cesarean deliveries in the United States.
Prevalence
  • Ranges from 3.5 to 4.6 per 1,000 births
  • Probability of resolution increases as gestational age at time of diagnosis and distance over the cervical os decreases.

Etiology and Pathophysiology

  • Uterine scarring may predispose due to interference with the natural growth of the placenta.
  • Placental bleeding is thought to occur when changes in the cervix and lower uterine segment apply shearing forces to the placental attachment site leading to partial detachment.
  • Bleeding is primarily maternal, although fetal bleeding may occur if a fetal vessel is disrupted.

Risk Factors

  • Previous placenta previa
  • Previous cesarean delivery
  • Multiple gestation
  • Multiparity
  • Advanced maternal age
  • Infertility treatment
  • Previous abortion
  • Previous intrauterine surgical procedure
  • Maternal smoking
  • Maternal cocaine use
  • Male fetus
  • Nonwhite race

General Prevention

No means of preventing placenta previa; may be able to decrease chances of vaginal bleeding due to activity modification

Commonly Associated Conditions

  • Placenta accreta complicated 1–5% of pregnancies with placenta previa.
  • Presence of placenta previa in the setting of prior cesarean delivery increases risk.
    • 11–25% with one previous cesarean delivery
    • 35–47% with two cesarean deliveries
    • 40% with three cesarean deliveries
    • 50–67% with four or more cesarean deliveries
  • High risk for need for hysterectomy at the time of cesarean delivery
  • Preterm labor and preterm rupture of membranes
  • Malpresentation
  • Intrauterine growth restriction
  • Respiratory distress syndrome
  • Anemia
  • Vasa previa and velamentous umbilical cord insertion
  • Congenital anomalies
  • Amniotic fluid embolism

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Citation

Stephens, Mark B., et al., editors. "Placenta Previa." 5-Minute Clinical Consult, 27th ed., Wolters Kluwer, 2019. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116460/all/Placenta_Previa.
Placenta Previa. In: Stephens MB, Golding J, Baldor RA, et al, eds. 5-Minute Clinical Consult. 27th ed. Wolters Kluwer; 2019. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116460/all/Placenta_Previa. Accessed April 24, 2019.
Placenta Previa. (2019). In Stephens, M. B., Golding, J., Baldor, R. A., & Domino, F. J. (Eds.), 5-Minute Clinical Consult. Available from https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116460/all/Placenta_Previa
Placenta Previa [Internet]. In: Stephens MB, Golding J, Baldor RA, Domino FJ, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2019. [cited 2019 April 24]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116460/all/Placenta_Previa.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Placenta Previa ID - 116460 ED - Stephens,Mark B, ED - Golding,Jeremy, ED - Baldor,Robert A, ED - Domino,Frank J, BT - 5-Minute Clinical Consult, Updating UR - https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/116460/all/Placenta_Previa PB - Wolters Kluwer ET - 27 DB - Medicine Central DP - Unbound Medicine ER -