Placenta Previa
Basics
Description
Description
- Placental tissue overlying or proximate to the internal cervical os
- Uterine enlargement and cervical dilation cause placental vessels near the cervix to tear, resulting in vaginal bleeding
- >90% of placenta previa diagnosed before 20 wk will migrate and have normal placental location at term
- Causes 20% of all antepartum hemorrhage
- Classification:
- Placenta previa: The internal cervical os is covered completely or partially by the placenta (previously referred to as total or partial previa, respectively)
- Low-lying placenta: The placenta is implanted in the lower uterine segment and the edge does not reach the internal os and remains outside a 2-cm wide perimeter
Etiology
Etiology
- Incidence: 3–5/1,000 births
- Maternal mortality: 0.03%
- Perinatal morbidity and mortality: Triple, due to preterm delivery
- Factors affecting location of implantation:
- Increased number of curettages from spontaneous or induced abortions
- Abnormal endometrial vascularization
- Delayed ovulation
- Risk factors:
- Multiparity (5% grand multiparous patients vs. 0.2% nulliparous)
- Multiple gestation (risk in twin pregnancy increases 30–40%)
- Prior C-section (up to 3× increase, increases with number of prior C-sections)
- Increased maternal age (0.1% age 12–19 yr, 0.9% age ≥35 yr)
- Previous placenta previa (4–8% recurrence)
- Smoking (2–4 times increase)
- Male fetus (14% increase)
- Assisted fertilization
- Associated conditions:
- Placenta accreta, increta, percreta (growth of placenta into uterine wall) occur in 5–10% of patients with placenta previa; sustained bleeding may require C-section hysterectomy
- Preterm premature rupture of membranes
- Amniotic fluid embolism; associated with pathologies of the placenta
- Vasa previa: Fetal vessels course through membranes and cover os
- Congenital anomalies
- Abnormal fetal presentation
- Higher risk for massive bleeding
- Short uterine cervical length in the third trimester
- Sinus venosus at margin of placenta
- Advanced maternal age at time of C-section
- Prior C-section
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Citation
Schaider, Jeffrey J., et al., editors. "Placenta Previa." 5-Minute Emergency Consult, 6th ed., Lippincott Williams & Wilkins, 2020. Emergency Central, emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307040/all/Placenta_Previa.
Placenta Previa. In: Schaider JJJ, Barkin RMR, Hayden SRS, et al, eds. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2020. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307040/all/Placenta_Previa. Accessed December 11, 2024.
Placenta Previa. (2020). In Schaider, J. J., Barkin, R. M., Hayden, S. R., Wolfe, R. E., Barkin, A. Z., Shayne, P., & Rosen, P. (Eds.), 5-Minute Emergency Consult (6th ed.). Lippincott Williams & Wilkins. https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307040/all/Placenta_Previa
Placenta Previa [Internet]. In: Schaider JJJ, Barkin RMR, Hayden SRS, Wolfe RER, Barkin AZA, Shayne PP, Rosen PP, editors. 5-Minute Emergency Consult. Lippincott Williams & Wilkins; 2020. [cited 2024 December 11]. Available from: https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307040/all/Placenta_Previa.
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