Vasa praevia
Encyclopedia
Vasa praevia is an obstetric complication defined as "fetal vessels crossing or running in close proximity to the inner cervical os. These vessels course within the membranes (unsupported by the umbilical cord or placental tissue) and are at risk of rupture when the supporting membranes rupture."
or may be joining an accessory (succenturiate) placental lobe to the main disk of the placenta. If these fetal vessels rupture the bleeding is from the fetoplacental circulation, and fetal exsanguination
will rapidly occur, leading to fetal death.
Etiology/Pathophysiology
Vasa previa is present when fetal vessels traverse the fetal membranes over the internal cervical os. These vessels may be from either a velamentous insertion of the umbilical cordVelamentous cord insertion
Velamentous cord insertion is an abnormal condition during pregnancy. Normally, the umbilical cord inserts into the middle of the placenta as it develops. In velamentous cord insertion, the umbilical cord inserts into the fetal membranes , then travels within the membranes to the placenta...
or may be joining an accessory (succenturiate) placental lobe to the main disk of the placenta. If these fetal vessels rupture the bleeding is from the fetoplacental circulation, and fetal exsanguination
Exsanguination
Exsanguination is the fatal process of hypovolemia , to a degree sufficient enough to cause death. One does not have to lose literally all of one's blood to cause death...
will rapidly occur, leading to fetal death.
Risk Factors
Vasa previa is seen more commonly with velamentous insertion of the umbilical cord, accessory placental lobes (succenturiate or bilobate placenta), and multiple gestation.Diagnosis
- This is rarely confirmed before delivery but may be suspected when antenatal sono-gram with color-flow Doppler reveals a vessel crossing the membranes over the internal cervical os.
- The diagnosis is usually confirmed after delivery on examination of the placenta and fetal membranes.
- Most often the fetus is already dead when the diagnosis is made; because the blood loss (say 300ml) constitutes a major bulk of blood volume of the fetus (80-100ml/kg i.e. 300ml approx for a 3kg fetus).