Which of the following complications is MOST likely to be associated with vasa previa?
- □ (A) Maternal hemorrhage
- □ (B) Placental abruption
- □ (C) Fetal hemorrhage
Vasa previa (Figure) is a velamentous insertion of the fetal vessels overlying the cervical os ahead of the fetal presenting part. This leaves the fetal vessels unprotected by the placenta or umbilical cord and at risk of being compressed by the fetal presenting part or disrupted during rupture of the fetal membranes. There is a high risk of fetal mortality due to exsanguination, as the blood volume of the term fetus is only 80 to 100 mL/kg. Immediate cesarean delivery is required, with the largest focus being on expedient delivery of the fetus and subsequent volume resuscitation of the fetus with colloid, balanced salt solutions, or blood transfusion.
The two main causes of vasa previa are velamentous insertions (where the cord inserts directly into the membranes, leaving unprotected vessels running to the placenta) and vessels crossing between lobes of the placenta, such as in bilobate (succenturiate) placentas. The incidence of vasa previa is between 0.02% and 0.04% of pregnancies. The risk factors for vasa previa include placental accessory lobes, multiple gestation, in vitro fertilization, and the presence of a low-lying placenta or placenta previa during the second trimester. When a diagnosis of vasa previa is made antenatally, the decision regarding the timing of delivery is based on fetal lung maturation and the risk of vessel rupture if the pregnancy continues. Many experts advocate for hospitalization at 32 weeks gestation, with a goal of delivery at 34 to 35 weeks. Neonatal mortality rates have been found to be 3% when vasa previa was diagnosed antenatally and 56% when it was not.
Once vessel rupture has occurred, there is only a short amount of time until fetal exsanguination due to the small blood volume of the fetus. Even trace amounts of vaginal bleeding need to be treated as an emergency. The choice of anesthetic technique depends on the urgency of the cesarean delivery. Often, a general anesthetic is required to expedite delivery of the fetus.
Clinically significant maternal hemorrhage is not typical in the presence of vasa previa. Placental abruption occurs when there is a complete or partial separation of the placenta from the decidua basalis prior to delivery of the fetus; this is not associated with vasa previa.
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