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.
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!