(vasa previa AE
) 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.
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 cord 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.
These vessels may be torn at the time of labor
or when the membranes rupture. It has a high fetal mortality because of the bleeding that follows.
The classic triad are membrane rupture followed immediately by painless vaginal bleeding and fetal bradycardia.
Vasa previa is seen more commonly with velamentous insertion of the umbilical cord, accessory placental lobes, and multiple gestation.
- 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 foetus is already dead when the diagnosis is made; because the blood loss (say 300ml) constitutes a major bulk of blood volume of the foetus (80-100ml/kg i.e. 300ml approx for a 3kg foetus).
with an emergency cesarean delivery is usually indicated.