Vasa previa involves fetal vessels in the membranes running over or in close proximity to the internal os of the cervix. This puts the vessels at risk of injury if the membranes rupture and can lead to exsanguination and fetal death.
Vasa previa is frequently associated with velamentous umbilical cord insertions. This involves the cord inserting into the chorioamniotic membrane rather than the placenta, which leads to fetal vessels traveling to the placenta unprotected by Wharton's jelly.
Placental abnormalities such as a bilobate or succenturiate placenta is a variation of placental morphology with one or more accessory lobes developing separately from the main placental body. This can lead to vasa previa, placenta previa, and retained placental tissue.
Multiparity, or a female who has carried more than one fetus > 20 weeks of gestation is associated with a greater risk of vasa previa.
The triad of symptoms with vasa previa involves membrane rupture, painless vaginal bleeding, and fetal bradycardia or fetal death.
The painless vaginal bleeding (fetal blood) occurs suddenly after membrane rupture.
Fetal distress includes fetal bradycardia (<110 bpm), decelerations or sinusoidal pattern on fetal heart tracings. Fetal death can quickly occur through exsanguination or asphyxiation if fetal vessels are compressed during labor.
A transabdominal or transvaginal U/S with color doppler shows fetal vessels overlying the internal os and decreased blood flow within fetal vessels.
An emergency C-section is usually indicated if there are signs of fetal distress.
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