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Posts Tagged ‘Placenta’

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.

previa.gif

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

good-velam.jpg

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.

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I have been asked by Alice to do a piece about ‘placenta papyrae’, I think she is referring to something variously called the vanishing twin, fetus papyraceous, or fetus compressus, my Mother had an example of this in a kitchen cupboard at home! Firstly, my Mother was a midwife, an early incarnation of a community midwife, bike and all. Secondly, our home was not cluttered with jars containing interesting specimens, just wonderful midwifery and obstetric textbooks with images guaranteed to stimulate a developing mind, this was the only pathological example I can remember. Her story goes that she attended a twin birth, at home, and when examining the placenta found this little ‘mummified’ fetus which she then kept in the bottle with some preserving fluid at home. As you can imagine I found this hugely interesting, I can remember from quite a young age climbing on to the kitchen work-surface to open the wall cupboard so I could sit and marvel at this strange little ‘alien’. It must have been about 3 inches long, it was a creamy colour, my recollection is that it looked like bone and was almost completely flat, with a large bluish dot where the eye should have been. I have no idea where it is now, I just hope it wasn’t left in the cupboard when she moved!What is it then? Well the first name I wrote gives a clue, a vanishing twin. As people are aware a great many more pregnancies begin as a twin one than end as one.  S. Levi, who studied over 6,000 early pregnancies sonographically, found that of the 188 sets of twins identified, only 86 sets were delivered as twins. From this it was inferred that the others had “vanished.” also   “Review of the sonographic findings of 1000 pregnancies with viable gestations in the first trimester revealed a minimum incidence of twinning of 3.29%. Of these, 21.9% demonstrated the “vanishing twin” phenomenon,” (Am J Obset Gynecol 1986;155:14-9.) Not all vanishing twins will become a fetus papyraceous as this ‘mummifying’ of a dead fetus is most likely to occur if the pregnancy has reached between 15 – 20 weeks.

How does it happen? Basically one, or more, of the feti in a multiple pregnancy dies and the fluid component of their body is absorbed, resulting in the mummification, but due to the bones being reasonably well developed by this gestation the fetus continues to maintain a recognisable shape, it is then compressed by the growing twin leading to the flattening. Hereis an interesting case, with picture, where one live baby was born and two fetus papyraceous were found, originally a triplet pregnancy.

Does this cause any problems for the surviving twin? There is evidence that it may, in some cases. The problems are not generally caused by the development of a fetus papraceous but by the death of the other baby. It may be that there were placental issues and in the case of identical, or uniovular, twins these would then have repercussions for the surviving twin. The change in the blood flow dynamics may also affect the twin that remains, studies have indicated that there is an increase in the incidence of cerebral palsy in the surviving twin, generally though this seems to be more prevalent if the death had occurred after 20 weeks of pregnancy(http://findarticles.com/p/articles/mi_m0CYD/is_17_35/ai_65538238). I have also found reports of a case where the mummified twin is blocking the cervix and so obstructs labour, my comment on this would be that the placenta must have been quite low-lying in the first place so this was a fortuitous event! There are other problems which may affect a surviving twin, the link to Early Path Medical Consultations (below)is quite informative about these.

I have only ever found one fetus papyraceous when examining a placenta, and it looked nothing like a fetus, it was almost discoid and at first I thought it was an area of calcification, the surviving twin was healthy, the parents were told about it and since the woman had experienced a bleed at 14 weeks they felt that this gave them an explanation.

papyrus-c.jpg Scanned from an old copy of ‘Obstetrics and the Newborn’. Beischer and McKay. This is a far larger fetus than generally seen and less mummified.

fetus-pap-with-text.jpg   This is far more representative but is as the result of ‘feticide’ in a multiple pregnancy so in fact is not a ‘vanishing twin’. The text accompanying this can be found here, Early Path Medical Consultations.

Alice asked two specific questions:-

Is it current practice to inform parents? Yes. Parents should be informed as there may be implications for the surviving twin. Also, the discovery of the vanished twin would be recorded in the clinical notes which the Mother would have access to, so it would be better that had been previously discussed with her and her partner.

What is the incidence? Rates quoted appear to be worldwide where articles I’ve read suggest that it ranges from 1:17,000 – 1:20,000 live births. With regad to the UK, the only reference I could find within UK statistics was 1 occurance in the CESDI 2001 report. 

If anyone wants to know more I would recommend this page on the FetusNet website.

Hope this has been of interest. If anyone would like me to ramble on about anything else midwifery related I would love to hear from you, especially over the next few weeks when I shall be kicking my heels until I am fit for work!

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