Vasa praevia Flashcards
Definition
Cause of antepartum haemorrhage ( bleeding > 24 weeks ) which occurs when the foetal blood vessels cross the internal cervical os, these vessels are unprotected by the umbilical cord or placental tissue and exposed = prone to haemorrhage when the amniotic membranes rupture
What are the fetal membranes
Surround the amniotic cavity and developing fetus
- Consist of two umbilical arteries and single umbilical vein
Physiology
Umbilical cord containing the fetal vessels (umbilical arteries and vein) inserts directly into the placenta. The fetal vessels are always protected, either by the umbilical cord or by the placenta. The umbilical cord contains Wharton’s jelly = layer of soft connective tissue that surrounds the blood vessels in the umbilical cord, offering protection.
Pathophysiology
Fetal vessels are exposed, outside the protection of the umbilical cord or the placenta.
- Fetal vessels travel through the chorioamniotic membranes, and pass across the internal cervical os (the inner opening of the cervix).
- These exposed vessels are prone to bleeding, particularly when the membranes are ruptured during labour and at birth. This can lead to dramatic fetal blood loss and death
Type 1 vasa pravia
- The fetal vessels are exposied as a velamentous umbilical cord
Type 2 vasa praevia
The fetal vessels are exposed as they travel to an accessory placental lobe
Risk factors
Low lying placenta
IVF pregnancy
Multiple pregnancy
Presentation
Antepartum haemorrhage = with bleeding during the 2nd or 3rd trimester of pregnancy
Diagnosis
USS during pregnancy
- ideal scenario to allow a planned section to reduce risk of haemorrhage
- though not reliable - often not possible to diagnose antenatally
- Detected by vaginal examination during labour, when pulsating fetal vessals are seen in the membranes through the dilated cervix
- May be detected during labour when fetal distress and dark-red bleeding occur following rupture of the membranes. V.high fetal mortality, even with emergency c-section.
Treatment ASx
RCOG guidelines (2018) recommend:
- Corticosteroids, given from 32 weeks gestation to mature the fetal lungs
- Elective caesarean section, planned for 34 – 36 weeks gestation
Treatment antepartum haemorrhage
Emergency c-section is required to deliver the fetus before death occurs.
- After stillbirth or unexplained fetal compromise during delivery, the placenta is examined for evidence of vasa praevia as a possible cause.