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Can placenta previa cause fetal blood loss?

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Based on the textbook sources, here is a thorough answer:

Placenta Previa and Fetal Blood Loss

The short answer: yes, but fetal blood loss is not the primary concern — maternal hemorrhage dominates. However, fetal blood loss can and does occur through specific mechanisms.

Mechanism of Bleeding in Placenta Previa

Placenta previa occurs when the placenta implants over the cervical os. Bleeding arises when marginal placental vessels in the lower uterine segment are torn as the lower uterine wall elongates or the cervix dilates near delivery. — Rosen's Emergency Medicine, p. 3354

Can the Fetus Lose Blood?

Yes, through two main pathways:
  1. Fetomaternal hemorrhage (FMH): Disruption of placental vessels can allow fetal blood to cross into maternal circulation. This is more classically associated with placental abruption, but any antepartum hemorrhage involving placental separation — including previa — can result in FMH. — Rosen's Emergency Medicine, p. 3356
  2. Vasa previa (a related but distinct condition): When fetal vessels traverse the membranes over the cervical os (vasa previa), rupture of these vessels causes direct fetal blood loss — not maternal. This is rapidly life-threatening to the fetus because total fetal blood volume is small (~80–100 mL/kg). The key distinguishing feature is that bleeding in vasa previa is fetal blood. — Creasy & Resnik's Maternal-Fetal Medicine, p. [block 10]

Severity and Clinical Impact

  • Central/total previa carries the highest risk, potentially causing exsanguination for both fetus and mother. — Rosen's Emergency Medicine, p. 3355
  • Blood loss requiring transfusion can occur in placenta previa cases. The fetus may develop distress from:
    • Loss of placental blood flow (impaired uteroplacental perfusion)
    • Maternal hemodynamic compromise reducing fetal oxygen delivery
    • Direct fetal blood loss via fetomaternal hemorrhage

Clinical Pearl

In Rh-negative mothers with antepartum hemorrhage from previa, 300 µg Rh immune globulin should be given within 72 hours if routine prophylaxis has not yet been administered — because fetomaternal hemorrhage (with fetal RBC crossing into maternal blood) may have occurred. — Rosen's Emergency Medicine, p. 3356
Summary: Placenta previa primarily causes maternal hemorrhage, but fetal blood loss is possible via fetomaternal hemorrhage and, when co-existing vasa previa is present, via direct fetal vessel rupture — the latter being an obstetric emergency with high fetal mortality if not rapidly delivered.
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