Vasa praevia is a condition that affects about one pregnancy in every 2000-2500 women. It involves the position of the placenta and/or the umbilical cord.
In a normal pregnancy, the umbilical cord inserts into the middle of the placenta as the placenta and the cord develop. In vasa praevia, the cord is closer to the edge, leaving blood vessels exposed. It also describes when the placenta and/or the baby’s umbilical cord are in a position that obstructs the baby’s descent down the birth canal.
The result is that the blood vessels of the placenta and/or cord are unprotected, and when the cervix starts to dilate at the start of labour, there is a serious risk of rupture. This means the baby can lose a great deal of blood, and may die during labour or shortly after birth.
There is a higher incidence of vasa praevia if:
- The baby is conceived by IVF.
- The placenta is low-lying (placenta praevia).
- There has been any bleeding in pregnancy.
- It is a multiple pregnancy.
- The mother has had a previous caesarean section, or any previous surgery on the uterus.
- There is a velamentous insertion – this means the umbilical cord inserts instead into the membranes surrounding the foetus, and then travels to the placenta. The blood vessels of the cord are unprotected, and they are at a high risk of rupture.
- The placenta has one or more succenturiate lobes – this means further ‘bits’ of placenta, attached by blood vessels to the main part of the placenta.
If a woman with vasa praevia is diagnosed in time, and she has her baby by caesarean section, then the risks of vasa praevia are greatly reduced.
Vasa praevia may be diagnosed by a colour Doppler ultrasound scan, though the diagnosis is not simple and special training is needed to interpret the scan.
The Royal College of Obstetricians and Gynaecologists report that, in some centres, this scan is offered to women with a higher risk of the condition. So far, there is insufficient evidence to justify the offer of colour Doppler to all pregnant women. The UK National Screening Committee does not recommend a national screening programme at this stage of knowledge. Research is ongoing to develop more understanding, and to see which women and babies are likely to benefit from screening.
Page last updated: 12 May 2014
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You can find out about this condition from the UK charity, Vasa Praevia.
Guidelines from The Royal College of Obstetricians and Gynaecologists: Placenta Praevia, Placenta Praevia Accreta and Vasa Praevia: Diagnosis and Management (Green-top 27)