Vasa Previa



What is Vasa Praevia?

  • Vasa Praevia occurs when one or more of the baby’s placental or umbilical blood vessels across the entrance to the birth canal beneath the baby.
  • When the cervix dilates or the membranes rupture, the unprotected vessels can tear, causing rapid fetal haemorrhage.
  • When the baby drops into the pelvis, the vessels can be compressed, compromising the baby’s blood supply and causing oxygen deprivation.


  • It is thought that vasa praevia occurs in approximately 1:2,500 births.
  • If the condition is not diagnosed prenatally, the fetal mortality rate is estimated to be as high as 95%.
  • In cases diagnosed prenatally (absent other congenital defect) the infant survival rate is 100%.
  • VASA PRAEVIA Raising Awareness are not aware of any prenatally diagnosed case which has resulted in the loss of the infant
  • NB. In IVF pregnancies the frequency is 1:300


  • Diagnosis is made by ultrasound using colour Doppler
  • During any anomaly scan the position of the placenta and the placental insertion of the umbilical cord should be recorded (i.e. whether the cord is centrally inserted, marginally inserted, a velamentous insertion or vasa praevia etc.).
  • In all cases where the placenta is low lying and/or the where the insertion of the umbilical cord is not central these cases must be referred for further diagnostic testing.
  • Additionally, all women presenting with warning signs or within the risk groups above should be scanned using transvaginal colour Doppler ultrasound again to specifically locate the placental-umbilical cord connection (see algorithm below).
  • If you suspect vasa praevia and you are not proficient in the use of colour Doppler ultrasound you should refer the patient to some one suitably qualified to make the diagnosis (see – What Next?)
  • Recent studies have shown that when vasa plaevia prenatally diagnosed, and a proper management plan is followed, the infant survival rate (absent any other congenital defect) is 100%-
  • The Royal College of Obstetricians and Gynaecologists have recently announced that they will be amending the current guidelines on the diagnosis and management of placenta praevia and placenta praevia accreta to specifically include advice on the diagnosis and recommendations of vasa praevia.

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