Placenta previa

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Placenta Previa - Low-Lying Intruder

  • Pathophysiology: Placenta implants over or near the internal cervical os. Types: complete, partial, marginal, or low-lying.
  • Clinical Presentation: Sudden, painless, bright red vaginal bleeding, typically after 20 weeks gestation. Uterus is soft and non-tender.
  • Risk Factors: Prior C-section, multiparity, advanced maternal age (>35), prior previa.
  • Diagnosis & Management:
    • Transvaginal ultrasound is the gold standard for diagnosis.
    • ⚠️ NO digital vaginal or speculum exams.
    • C-section delivery is indicated, usually at 36-37 weeks.

⭐ The classic triad is painless bleeding, a soft non-tender uterus, and reassuring fetal heart tones. Absence of pain is a key feature distinguishing it from placental abruption.

Sagittal ultrasound of placenta previa

Risk Factors & Presentation - Red Alert Antepartum

  • Risk Factors:

    • Prior C-section or other uterine surgery
    • Multiparity & advanced maternal age (> 35 yrs)
    • Cocaine use or smoking
    • Prior placenta previa
  • Clinical Picture:

    • Sudden, painless, bright red vaginal bleeding
    • Typically occurs after 28 weeks gestation
    • Uterus is soft, relaxed, and non-tender
    • Fetal heart tones usually reassuring initially

Placenta previa: marginal, partial, complete, and central

Warning: Digital or speculum vaginal examination is absolutely contraindicated as it can provoke catastrophic hemorrhage. Diagnosis is made by ultrasound.

Diagnosis - Ultrasound Unveiling

  • Initial Test: Transabdominal ultrasound.
  • Gold Standard: Transvaginal ultrasound (TVS) is safe & more accurate for precise localization.
  • Follow-up: Repeat scan at ~32 weeks; many early previas resolve via "placental migration."

⭐ A digital vaginal exam is contraindicated if placenta previa is suspected until it has been ruled out by ultrasound.

Transvaginal ultrasound: complete placenta previa

Management - Watchful Waiting Game

  • Indication: Preterm gestation (< 36-37 weeks) with a hemodynamically stable mother and reassuring fetal status.
  • Core Strategy: Inpatient observation, especially after a bleeding episode.

Cardiotocography showing fetal well-being

  • Key Interventions:
    • Corticosteroids (Betamethasone): Administer if gestational age is < 34 weeks to promote fetal lung maturity.
    • Strict Pelvic Rest: No vaginal exams (digital or speculum) and no intercourse.
    • Tocolysis (e.g., Magnesium Sulfate): ⚠️ Used cautiously for short-term uterine quiescence, primarily to allow corticosteroids to take effect.
    • Anemia Correction: Maintain maternal hematocrit > 30%.

⭐ Elective cesarean delivery is planned for 36 0/7 to 37 6/7 weeks, even in asymptomatic cases, to minimize the risk of hemorrhage from spontaneous labor.

Complications & Vasa Previa - Dangerous Liaisons

  • Maternal: Risk of massive hemorrhage (may necessitate hysterectomy). Placenta accreta spectrum risk ↑ with prior C-sections.
  • Fetal: Preterm birth, IUGR, and fetal anemia.
  • Vasa Previa: A related emergency where unprotected fetal vessels run over the cervical os. Membrane rupture can tear these vessels, causing rapid fetal exsanguination.

Vasa Previa Triad: Rupture of membranes, painless vaginal bleeding, and subsequent fetal bradycardia or a sinusoidal heart rate pattern.

Vasa Previa Type 1: Fetal vessels near cervix

High‑Yield Points - ⚡ Biggest Takeaways

  • Painless, bright red vaginal bleeding in the third trimester is the classic presentation.
  • The placenta implants over or near the internal cervical os.
  • Major risk factors include prior cesarean delivery, multiparity, and advanced maternal age.
  • Transvaginal ultrasound is the gold standard for diagnosis; transabdominal is used for initial screening.
  • Digital vaginal examination is absolutely contraindicated due to the risk of catastrophic hemorrhage.
  • Management is typically a planned cesarean delivery at 36-37 weeks.

Practice Questions: Placenta previa

Test your understanding with these related questions

A 26-year-old Caucasian G1 presents at 35 weeks gestation with mild vaginal bleeding. She reports no abdominal pain or uterine contractions. She received no prenatal care after 20 weeks gestation because she was traveling. Prior to the current pregnancy, she used oral contraception. At 22 years of age she underwent a cervical polypectomy. She has a 5 pack-year smoking history. The blood pressure is 115/70 mmHg, the heart rate is 88/min, the respiratory rate is 14/min, and the temperature is 36.7℃ (98℉). Abdominal palpation reveals no uterine tenderness or contractions. The fundus is palpable between the umbilicus and the xiphoid process. An ultrasound exam shows placental extension over the internal cervical os. Which of the following factors present in this patient is the risk factor for her condition?

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Flashcards: Placenta previa

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Placental _____ is the premature separation of the placenta from the uterine wall (decidua) prior to delivery of fetus

TAP TO REVEAL ANSWER

Placental _____ is the premature separation of the placenta from the uterine wall (decidua) prior to delivery of fetus

abruption

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