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Difficulty: Very hardLabor, Delivery, and Puerperium

A 28-year-old G2P1 woman at 36 weeks gestation presents to the labor triage unit complaining of mild, irregular abdominal cramping. Two hours ago, she was given intravenous fentanyl at an outside clinic for severe back pain. Her prenatal course was notable for a second-trimester anatomy ultrasound revealing a bilobed placenta. Shortly after admission, she experiences a sudden rush of clear fluid from her vagina, followed immediately by a gush of bright red blood. She denies any sharp or severe abdominal pain. Maternal vital signs are: blood pressure 118/76 mmHg, heart rate 86/min, and temperature 37.1°C (98.8°F). The abdomen is soft, non-tender, and without guarding. Fetal heart rate monitoring demonstrates a baseline of 150/min. The tracing exhibits a smooth, undulating, sine-wave-like pattern with a frequency of 3 to 4 cycles per minute, completely absent beat-to-beat variability, and no accelerations. This pattern has persisted for 25 minutes. A sterile speculum examination shows active bleeding pooling in the posterior fornix. Which of the following is the most appropriate next step in management?

  1. Proceed to emergent cesarean deliveryAnswer
  2. B
    Administer maternal intravenous fluids and oxygen
  3. C
    Perform an amnioinfusion
  4. D
    Continue continuous fetal monitoring and expectant management
  5. E
    Administer subcutaneous terbutaline

Answer

Proceed to emergent cesarean delivery
The correct step in management is to proceed to an emergent cesarean delivery. This patient's clinical presentation is highly specific for ruptured vasa previa. Vasa previa occurs when unprotected fetal blood vessels (often associated with a velamentous cord insertion or connecting a bilobed/succenturiate placenta) run through the amniotic membranes directly over the internal cervical os. When the amniotic membranes rupture, these fragile vessels can easily tear, leading to rapid fetal exsanguination. The classic triad includes a membrane rupture, painless vaginal bleeding, and fetal bradycardia or a sinusoidal fetal heart rate pattern. The sinusoidal pattern—characterized by a smooth, undulating wave of 3 to 5 cycles per minute with absent beat-to-beat variability—is a dire sign of severe fetal anemia and hypovolemia. Although the recent administration of fentanyl can occasionally cause a temporary, benign 'pseudosinusoidal' pattern, the presence of active bleeding and a bilobed placenta confirms this is a true, life-threatening sinusoidal rhythm. Because the bleeding is fetal in origin and the total fetal blood volume is extremely small, death can occur within minutes. Immediate emergent cesarean delivery is the only definitive and life-saving management.

Step-by-Step Solution

1
Identify the maternal risk factors and clinical presentation.
The patient has a bilobed placenta, a major risk factor for vasa previa. She presents with painless, bright red bleeding immediately following the rupture of membranes.
Correlating the structural placental anomaly with the exact timing of the bleeding (ROM) isolates the source of the hemorrhage to aberrant fetal vessels crossing the cervical os.
2
Interpret the fetal heart rate (FHR) tracing in the context of the clinical picture.
The FHR shows a true sinusoidal pattern (smooth sine-wave, 3-4 cycles/min, absent beat-to-beat variability, no accelerations).
A sinusoidal pattern indicates severe fetal anemia and hypoxia. While the recent fentanyl dose can cause a benign pseudosinusoidal pattern, the concurrent ROM and acute hemorrhage confirm this is a true sinusoidal pattern due to rapid fetal exsanguination.
3
Determine the most appropriate management.
Immediate surgical intervention is required.
Ruptured vasa previa is a catastrophic obstetric emergency. Fetal blood volume is very small, and exsanguination occurs rapidly, necessitating an emergent cesarean delivery to save the fetus.

Key Concept

Ruptured vasa previa typically presents with painless vaginal bleeding immediately following rupture of membranes, accompanied by a true sinusoidal fetal heart rate pattern indicating fetal exsanguination. The required management is emergent cesarean delivery.
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Topics

Labor, Delivery, and Puerperium

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