Vasa Previa – a midwives dictionary definition is ‘Vessels in front of the presenting part. A rare condition of velamentous insertion of the umbilical cord, usually with a degree of placenta previa, in which the vessels in the membranes are lying in front of the presenting part. When the membranes rupture there is a risk of compression of, or even haemorrhage from these vessels leading to hypoxia or haemorrhage to the child.I would add to this ‘where there is a succenturiate lobe to the placenta’.
Quite a lot of medical jargon here so I’m going to get that out of the way first and explaining all these should go a long way to explaining vasa previa.
Vessels – blood vessels of the umbilical cord.
Presenting part – here they are talking about what part of the baby is coming first, generally the head.
Velamentous – In a normal placenta the cord and the vessels go right up to the surface of the placenta before branching off, with a velamentous insertion the blood vessels branch off before reaching the placenta so are therefore exposed within the membranes.
Placenta previa – Placenta previa is when the placenta attaches to the wall of the uterus in the lower portion of the uterus and covers all or part of the cervix. It is found in about 1:200 pregnancies at term ( 37 – 42 weeks). It is observed far more frequently on 20 week scans but on re-scan at 34 – 36 weeks the placenta has moved away from the cervix.
Different types of placenta previa
Membranes rupture – Waters break, either by themselves or with a little help.
Hypoxia – Baby does not receive enough oxygen due to the pressure on the blood vessels.
Haemorrhage – The blood carried within the umbilical cord is the baby’s. Think of the cord as an extension of baby, rather like the tubes in a dialysis machine or a heart-bypass, and you can understand why a breaking of these would lead to the baby having a huge blood loss, but whilst still inside it’s Mother’s womb.
Succenturiate – the placenta has an extra, separate piece to it. Often this is immediately adjacent,, so is not as much of a concern for vasa previa, but it can be some distance away and so have blood vessels which cross over the membranes connecting it to the main body of the placenta.
Photo of Vasa Previa
So what is the incidence of vasa previa? Stats vary, as usual, but there seems to be a consensus of around 1: 2,000 – 1:3,000 pregnancies.
How is it discovered? It can be detected on a 20 week scan, but it can be easy to miss, if the woman is overweight, has a bladder that is obscuring the view or the problem blood vessels are in a position where they can not be seen, so unfortunately some cases are not detected until the waters break and there is blood. When I say blood I don’t mean a very slight pinky tinge, that is normal, I mean when the fluid looks like fresh blood. There are clues though that there may be vasa previa, a low-lying placenta, a placenta that has an extra lobe (succenturiate), the incidence appears to be higher in IVF pregnancies, women who smoke, multiple pregnancies, and have a previous history of the condition so these cases would be thoroughly investigated
What can be done? Diagnosis is the most important step. Once diagnosed then decisions can be made about time and mode of birth which, studies have shown leads to a good outcome. Recently a surgeon has reported success with treating this problem by laser surgery to the blood vessels. However, this case was where there was an extra lobe to the placenta, not where the problem was a velamentous insertion. Good article to read though for more information.
How dangerous is it? Well, if it’s not detected then the death rate for baby can be as high as 95% but, if it’s found antenatally then, as long as there are not any other problems, the survival rate is 100%.
Wonderful website here, UK Vasa Previa Awareness.
Thank you to Mother of the Bride for suggesting this topic. If anyone else has any ideas for a post please let me know.