Down Syndrome Community
Genetics - specifically Down's syndrome risk detection
About This Community:

This forum is for questions and support regarding Down Syndrome issues such as Dental Problems, Communication Problems, Developmental Disabilities, Hearing Loss, Hypothyroidism, Immune System Problems, Learning Disabilities, Joint Problems, Muscle Weakness, Respiratory Disorders, Seizures, Sleep Apnea, Weight Problems.

Font Size:
A
A
A
Background:
Blank
Blank
Blank
Blank Blank

Genetics - specifically Down's syndrome risk detection

Hi - I am 39 and pregnant with identical twins (MONO/Dia)  We had a 12 week pre-screen ultrasound which showed 1.4 NT Twin A and 1.8 NT Twin B.  I did the blood work as well which has returned a risk for Down's syndrome.   They said Twin A 1:310. B 1:70.  I guess I am wondering with Identical twins if it is possible to have one with DS and one with out.  I am also curious as to how they could determine 2 separate readings??  I am meeting with a genetic counselor on Monday.  We are considering Amnio but I was also wondering what else could be done (exhaust all tests) before Amnio?  Any thoughts?  What other 'soft markers do they look at?'
Related Discussions
8 Comments Post a Comment
Blank
1227139_tn?1367231533
Hello LindyLou71,  (Just so you know additionally, I have a son with Down syndrome and I am an appointed guide from the hospital genetics department - diagnosis of Down syndrome)

This is a very interesting question because with identical twins (and since you know they are mono/di meaning from a single egg which split and became two identical embryo's from one - with one sperm) which share the same placenta but separate amniotic sacs they can have some differences but usually not genetically.
"Most of the time in identical twins the zygote will split after 2 days, resulting in a shared placenta, but two separate sacs. These are called monochorionic, diamniotic ('mono/di') twins.These twins are very similar genetically, and share a single afterbirth."

For this, you must consult with the genetics doctor regarding the possibility of a mono/di twin being able to have Down syndrome and the other not.  In my realm of genetics I had never heard of this being possible.  Research says; mono-zygotic twins are genetically same (because of mitotic division of the zygote) but can have similarity differences such as fingerprints and birthmarks.

HOWEVER I did find a few medical journals that did confirm that the possibility of a mono-zygotic set of twins having different karyotypes (chromosomal arrangements):

"Abstract

A chromosomal abnormality in one of the fetuses of a monozygotic twin pregnancy is a rare phenomenon. In the prenatal unit of our cytogenetics laboratory we have recently come across two such heterokaryotypic twin pregnancies. In both cases ultrasound abnormalities were detected in one fetus of each twin pair. Chromosomal analysis showed that one twin pregnancy was discordant for trisomy 21 and the other for 45,X. Ultrasonographic examination suggested a monochorionic twin pregnancy in each case and DNA studies confirmed that both sets of twins were monozygotic. Both pregnancies were terminated. Biopsies taken from different sites of the placentas showed chromosomal mosaicism in both cases. There was no clear correlation between the karyotype found close to the site of the umbilical cord insertion in the placenta and the karyotype of the fetus. Sampling of amniotic fluid from both sacs is recommended in diamniotic twin pregnancies if one (or both) of the fetuses has ultrasound abnormalities, even if the twins are apparently monochorionic."

So the possibility does exist but it is EXTREMELY RARE.  

I have a complete listing of markers.  If you are interested - please message me directly.  My list is from my new resource website and it wont fit entirely in one comment message post here.  I can message it to you.  They do look at a number of soft and hard markers.  There is a whole set of factors that are looked at as medical protocols.  In my website, (which I have been working on for the last few months) I explain all the possible markers, testing and screening that you can choose to do, before deciding to have an amniocentesis.  But, in a case where the radiologists then suspect this rarity, an amniocentesis should be considered, that can confirm with absolution if one twin does have T21 (Down syndrome).  

The most important thing I want to also pass onto you, is that I have a lot of recent and positive information regarding Down syndrome (Ds) because there is so much outdated and incorrect information out there about Ds.  I have a blog as well that has quite a bit of information for you to review if you are interested.
http://welcometoourhouse-myjournal.blogspot.com

I hope that you will message me directly for the marker info that you mentioned your interest in.  When you do message me, just remind me of your post, and that you need the marker list from me  (so that I will remember).  I have many many requests for genetic information.

In addition to anything I have mentioned, please keep in mind, that while I or others may have extensive knowledge in many areas, you should always seek professional medical advice from your own physician, as it pertains to medical conditions or concerns.

Good luck, and if you have any other questions that I can help you with, please feel free to message me directly.

Sincerely,
Sandi (Dragon1973)
MedHelp Genetics Community Leader;
Children - Special Needs Community Leader;
Down syndrome Community Leader & Ds Group Forum Founder/Moderator
Blank
Avatar_n_tn
Hi - firstly - thanks for your awesome and detailed response.  My personal email I will send privately and would love the markers list to be prepared.  So I'll give you an update....

We met with the genetics counsellor at our local hospital.  Essentially the nurse at my OB's office was a bit off on the numbers.  The way they explained it to us was that without any testing based on age alone my ratio for multiple pregnancy and DS was 1:110 she said if you called there and they didn't know me from Adam they would give me this quote.  She also told me that the screen positive result was based solely on the Ultrasound readings.   That being said she told us that Twin A - NT 1.5mm Ratio 1:310 and Twin B NT 1.8mm Ratio 1:170 so basically the nurse omitted 100??? nice.  Anyways we are / have at this point beaten the original odds.  She said the differential between them stems from the .3 difference in the measurement.  They are truly identical without a doubt.  Her answer to this is NO if they are truly identical the chromosomal abnormality would occur prior to the split and they would both have it.  In her experience she has NEVER seen/heard of IDENTICAL twins where one has DS and the other one does.  I had seen some of the research out there but I think it is very very rare and the results are skewed.  Either way I understood what she meant.  She also told us that with Mono/Di twins the Amnio would have to be preformed 2 x.  One per side.  In our Twin case our twins are separated by a thin membrane and have separate placentas.  Apparently this is a good thing.  Limits the Twin to Twin transfusion thing and the membrane eliminates the cord entanglement of the other thing.  

Bottom line - I am feeling better.  It was hard to get the call at 3pm on a Friday afternoon.  I am frustrated by the fact that the info revealed to us wasn't quite accurate.  

I have seen a few of your posts and congrats on your beautiful baby boy.  I think you are an amazing woman.  I am 39 and I have a 22 month old and some days I find it a struggle.


Next step
week 15 quad screen, (MSS?), Week 18/19 - Level 2 ultrasound at the hospital with a sonographer/radiologist.  Based on those findings we may opt for Amnio.  I am hoping as a last result.  

Thx again.
Blank
1227139_tn?1367231533
Hi Linda!

You are most welcome and thank you for the positive compliments!  (I did receive your direct message also.)  I was certainly finding it hard to believe that identical Mono/Di twins could possibly have different chromosomal arrangements, thus my initial answer.  After my own in depth research, I found only one medical journal which stated a case where this happened, but I do believe that this circumstance involved a dynamic separation of the chromosomes affecting both twins in a very different way.  (One twin had 45 chromosomes and the other had 47).  I have no way to even verify that it ever occurred.  And in what we know scientifically, really when Mono/di twins are in question, the fact remains that genetically they must be identical in order to be identical twins!!  So, I am glad that the nurse corrected herself and the numbers.  

With a .3 mm measurement difference, the likiness is that the difference in measurement is from the technician, not the twin.  And there are so many technical formulae which allow for each different radiologist and their unique measurement abilities, so never will two measurements ever be the same and this proves that point.  But even if there was a minute millimetre difference in one twin from the other, (that wasn't from the inaccuracy of the technician, or the position of the baby) the fact remains that the measurement for the Nuchal Translucency changes as the baby grows.  Each, moment, minute, day and relative to the size of the fetus, means that measurement will change.  
The great news is that your babies measurements are actually wonderful, without knowing the median range measurement for your area (every location state to state, country to country is different) what you shared is quite good for measurements and also correlating risk odds.

At the end of the day, odds are just that.  A risk assessment which allows the screening to be compared to another set of statistics.  The results of those comparisons allows the doctors to refer you appropriately by protocol for next stage testing if required.  And ultimately with those numbers the choice would definitely be completely up to you.  (But only after you have your level 2 ultrasound to correlate).  My initial original maternal ratio for Ds was 1:385.  My ratio didn't change after my NT scan either, which came back as in normal range.  I often say to people who have high NT results that in comparison to me, the results can be misleading.  Families who worry about high numbers wishing that their numbers were low and normal have to understand that low results can equally end up with Down syndrome just as my son did.  So, it is all relative to understand that the numbers are just odds and risks, not definite determining facts.  And I think, for the most part - most mom's know that the only way to know definitively is by actual testing (instead of screening) such as Amniocentesis, CVS, or PUBS.

If anything, I took away a couple things from being in my own situation (as described above) are these facts:
1.  numbers are just numbers, to assess risk or odds for next stage screening or testing.  
2.  Thinking that normal numbers mean everything is just fine doesn't necessariy mean it is, and
3.  After thinking that things like this happen to other's and not me, wasn't obviously not realistic.

Something that I also mention to mom's who have NT scans done - avoid comparing your results to other moms with results.  NT ranges for "normal" differ around the world, and even state to state (province to province).  Countries have different median ranges, so it is impossible to compare what is normal or considered likely normal.  In order to know if your result is a concern, ensure you have your results and locations ranges.  Speak with your local genetics counsellor or genetics doctor.  Never look at your NT scan results singularly.  They are never taken as a singular measurement alone. They are correlated with other diagnostic screening.   Again, the only way to have a confirmed diagnosis is via actual chromosomal testing.  This can only be done by sampling tissues (CVS or PUBS) , fluids (Amnio) or blood from the baby (Blood test after birth).  Otherwise everything else is a screen test, designed to give likeliness or percentage of likeliness.

I hope this helps others down the road!  And if ever anyone has any questions, please do not hesitate to contact me directly!

Keep me posted Linda!

In addition to anything I have mentioned, please keep in mind, that while I or others may have extensive knowledge in many areas, you should always seek professional medical advice from your own physician, as it pertains to medical conditions or concerns.

Good luck, and if you have any other questions that I can help you with, please feel free to message me directly.

Sincerely,
Sandi (Dragon1973)
MedHelp Genetics Community Leader;
Children - Special Needs Community Leader;
Down syndrome Community Leader & Ds Group Forum Founder/Moderator
Blank
1501649_tn?1289325276
hi there!

amazing feedback and great to get so much understanding.

I do hope all had turned out for the better to all. x

I live in the UK and am pregnant with triplets, 2 of which are sharing 1 placenta but each with there own sack. Today we went for our 12 week Nuchal t -scan and turnes out 1 of the identical twins came out at 3.00 so not good for other twin. After dicussing with the dr. consultant we are are waiting 4 more weeks and then deciding on how to go forward.  Any feedback or anythign I should know that could help, we understande that DS is lower risk in twins aparently here in uk but it could be TTT, if so we were advised to reduce pregnancy in either case once determined or to investigate further and if TTT ti have a lazer divide both twins bloods from 1 placenta and hope all survive.

thanks again and look forward to hearing from you x

Margarita x
Blank
Avatar_f_tn
I am in a similar situation as you identical twin 2 soft markers on 1 .I will not do amnio I did a lot of searching and not getting anywhere info I'd like to now if u now more by now I didn't see any post since sept. Please help
Blank
1227139_tn?1367231533
Hello Pimpona80,

First please let me apologize for not responding back to your post.  Sometimes I do not get notifications regarding posts that I am "watching" and only happen to come across them in my readings only to learn that someone has asked a new question on an older post.  Can you give me any more information - as it has been a while since your post and I am sure you have had some further interaction with your doctors since your posting.

Feel free to message me directly, as those messages I seem to get immediately and not lost in cyber space.  Again, please accept my apologies for not seeing your post sooner.  I hope that while this time has passed, things are continuing well for you with your pregnancy.

In addition to anything I have mentioned, please keep in mind, that while I or others may have extensive knowledge in many areas, you should always seek professional medical advice from your own physician, as it pertains to medical conditions or concerns.

Good luck, and if you have any other questions that I can help you with, please feel free to message me directly.

Sincerely,
Sandi (Dragon1973)
MedHelp Genetics Community Leader;
Children - Special Needs Community Leader;
Down syndrome Community Leader & Ds Group Forum Founder/Moderator;
MTHFR Group Forum Founder/Moderator;
Pregnancy: June 2011 Community Leader
Blank
Avatar_m_tn
Hi Sandi,

Your posts are very helpful.  I as well, am carrying identical twins.  I am 15 week pregnant and I just came back from my doctor where she told me that my babies NT scan returned abnormal.  Baby A was at 2.5 and Baby B was at 2.3. I am 36 years old and she told me that my risk is 1/250.  Do you have any indication as to why the measurements would be off by 2mm?  She claimed that this could not have been human error.  I am freaking out right now and am not sure what to think at this point.

Thanks
Blank
Avatar_f_tn
I read your old post and wondered if you, indeed,  had on twin with DS and one without.  My daughter's OB/GYN told her that her testing (nearly 12 years ago) was elevated because she was carrying twins.  And she was, 2 girls, one with DS and one without.  The surprise of birth gave us a momentary cry and sniffle but, ya know, my two granddaughters are wonderful.  Different as night and day.  Chloe, with Down's, is the leader of the pack.  She is the alpha dog to the point that she dominates her 20 year old brother.  Trying to get a "retarded" educational system to understand that Chloe was a bright girl and was just slower than her sister has been hell.  If, if fact, you did have a DS child, fight like the devil to get the education that child deserves.  It is so important for their self esteem.
Blank
Post a Comment
To
Blank
Weight Tracker
Weight Tracker
Start Tracking Now
Down Syndrome Community Resources
RSS Expert Activity
233488_tn?1310696703
Blank
New Cannabis Article from NORTH Mag...
Jul 20 by John C Hagan III, MD, FACS, FAAOBlank
242532_tn?1269553979
Blank
3 Reasons Why You are Still Binge E...
Jul 14 by Roger Gould, M.D.Blank
242532_tn?1269553979
Blank
Emotional Eating: What Your Closet ...
Jul 09 by Roger Gould, M.D.Blank