Vasa praevia is a condition occurring in pregnancy where the foetal vessels (the umbilical arteries and umbilical vein) are exposed and run across the internal os. It carries a high foetal mortality rate (60%) if not diagnosed and the placental membranes rupture (either spontaneously or artificially), therefore it is an important condition to identify as well as prevent complications with through elective C-section (95% survival rate through this route).
🔢 Pathophysiology and classification
Normally, the foetal vessels are contained within the placental tissue itself and then the umbilical cord is the conduit connecting the placenta to the foetus. Within the cord there is a thick connective tissue made up of proteoglycans, glycosaminoglycans and hyaluronic acid. This connective tissue is known as Wharton’s jelly and its primary function is to protect the umbilical blood vessels.
Unfortunately, in instances of vasa praevia, these foetal vessels are not protected by the placenta or the cord and instead simply run through the chorioamniotic membranes. Without protection, it may be at risk of bleeding. This is especially true when the membranes themselves rupture (during labour).
There are 2 situations where the foetal vessels may be exposed, and this also can help denote the praevia as type I or type II:
- Velamentous umbilical cord insertion (type I) - this is when the umbilical cord itself inserts into the chorioamniotic membranes instead of the placenta. This leaves the vessels to travel through the remainder of the membranes and insert into the placenta.
- Succenturiate placenta (type II) - this is an accessory lobe of the placenta which connects to the main lobe of the placenta with the vessels connecting through the membranes.
⚠️ Risk factors
- Low lying placenta
- In-vitro fertilisation
- Multiple pregnancy
- Placental abnormalities
😷 Presentation
Most commonly vasa praevia is asymptomatic until labour where it can often be too late and result in haemorrhage. It may present with:
- Dark-red vaginal bleeding immediately after rupture of membranes - subsequently followed by acute foetal compromise.
- Antepartum haemorrhage in the second or third trimester.
- Pulsating foetal vessels on vaginal examination.
🔍 Investigations
A transabdominal and transvaginal Doppler ultrasound at the time of the foetal anomaly scan (18-20 weeks) is the best diagnostic method for vasa praevia and has greatly helped antenatal diagnostic accuracy. If identified, it is essential to confirm the persistence of vasa praevia within the third trimester of pregnancy as well.
Vaginal examination may identify pulsation of the foetal vessels which may warrant a scan itself.
🧰 Management
Women with identified vasa praevia should be offered:
- Planned C-section at 34-36 weeks gestation - this means the baby is preterm. Women may be prophylactically hospitalised at 30-32 weeks if they have multiple pregnancy, antenatal bleeding or any threatened premature labour.
- If there is premature rupture of membranes → perform emergency C-section without delay.
- Corticosteroid injections at 32 weeks gestation - for foetal lung maturation seeing as the baby is preterm.
🚨 Complications
- Preterm birth
- Foetal death