Fraternal twins sharing a placenta

Hi everyone, just wanted to say hi and introduce myself. My wife and I are expecting boy/girl twins in November and it's been a crazy rollercoaster ride for us since we first found out at 6 weeks.

At our first ultrasound, we were told that they were definitely identical because they were sharing a placenta and chorion (monochorionic). But as time went by, it was clear that one was a boy and one was a girl. So we did an amnio and DNA testing and had a rough few weeks where a number of possible scenarios played themselves over and over in our heads and conversations.

One of the possible scenarios was an abnormality in at least one twin's chromosomes - we learned a lot about the difference between gender phenotypes and genotypes, with Turner's Syndrome being one of the explanations (the girl loses the 46th chromosome and has only 45X). But the amnio came back with completely normal chromosomes.

Yesterday we just confirmed that they are dizygotic (fraternal). Our doctor tells us this is the world's first reported case of a monochorionic dizygotic pregnancy without any kind of fertility treatment (14 total ever reported cases). We're flabbergasted but also relieved that both babies are healthy, genetically normal and doing well.

So don't let anyone tell you that twins who are sharing a placenta and chorion MUST be identical. Apparently it is possible for the two eggs to fuse when they are only a few cells big, and develop just like identical twins would. So now that we can rest easy about that, we can now focus on getting ready for the twins! We have a one year old daughter already so at least have some notion of what to expect.

We're really glad this forum exists and look forward to meeting other twin parents!

Ryel

PS I thought I'd mention that my wife writes a blog for expecting moms called The Mama List (www.themamalist.com) so check it out sometime if you get a chance.

 

Wow, that is amazing!! Best of luck to you.

 

:wavey: Ryel and welcome to Twinstuff. Congratulations on your twins! :Clap: That is very interesting about your b/g twins, I've not heard of them being able to share a placenta. I'm glad that they are both doing well. :hug:

 

I have a high school friend (who is an obstetrician) and she has mono-di fraternal boys. In fact, when I told her we were having identical twin boys because they were sharing a placenta, she told me not to count on it and that the only way you can know *for certain* that they're identical is to do a DNA test. We know ours are boys, and we're expecting identical - I figure that time will eventually tell. In the meantime, we'll paint a fingernail or something.... Congratulations on your twins!

 

It could be that the placenta fused very early and its not technically a mo-di pregnancy. They then should not be able tell if it was fused or one placenta till after birth.

 

i have heard of placentas of the fraternal twins fusing, but never of them sharing the same one..i don't have that issue at all..one placenta is to the front, one to the back, it was pretty obvious even at 12 weeks that the babies were fraternal...congrats on your little ones, it'll be interesting to see what the placenta looks like once your little ones arrive!

 

Welcome to TS!!! Congrats on your b/g twins!

 

That is so interesting! To share a chorion and placenta yet be fraternal? Welcome to ts and i look forward to hearing more from you as time goes on! Good luck!

 

hello and thanks for all the replies and warm welcome... to TwinxesMom, our docs determined mono/di by the wall separating the two fetuses, which they said was 100% definitely just the two amnions and not a chorionic separation, just like identical twins. you're right, the placentas could have become fused early but in this case the fact that they are sharing a single chorion is what confirmed the mono/di scenario, with the amnio and zygosity testing confirming they are fraternal twins.

we are thinking that maybe this scenario is more common than people might think, and that it is either never caught or not reported. we're just happy to be carrying healthy babies at this point... now hoping for a straightforward birth. our first daughter was breech but was delivered naturally and drug-free so hoping for the same this time around.

 

Oh I forgot to mention, one of the interesting outcomes of this scenario is that our twins are sharing blood vessels just as identical twins do, but since they each have two different blood types, they are likely to be chimeric - each will carry the blood type of the other, including his or her own. (I can hear one of my friends saying, "damn nature, you strange!")

 

Amazing. Then are they at risk for TTTS since they share vessels?

 

yes exactly.

 

go look up what being a Chimera really is. not something i'd wish on any child more so b/g twins

 

Wow Ryel!!! I will pray for an easy pregnancy for your twins! Welcome o the forum and thanks for sharing ur experience with us.

 

Well chimerism takes many forms, some are more serious and life affecting than others. Blood chimerism is typically more of a novelty than anything that will affect the quality of their lives, (although it could make it easy for them to get away with criminal activity !) Could make transfusions interesting though. Interestingly, blood chimerism is quite common among cattle, carriers of which are called freemartins, but extremely rare in humans and other species.

 

here is a link to a paper on one of the very few reported cases of monochorionic dizygotic twins, very similar to ours except of course we didn't use any fertility treatment. the paper refers to other such twins but all with some kind of fertility treatment involved. the twins in this paper have blood chimerism but test normal in every other way.

they offer tentative explanations for how two eggs can fuse and share a single chorion, but as you can read, it's all pretty speculative.

http://humrep.oxfordjournals.org/cgi/reprint/dei379v1.pdf

 

Neato!

Welcome, I love the scientific talk.

 

Welcome to Twinstuff! :welcome:

 

Welcome to TS and Congratulations on your twins! Thank you for posting that article, I love to educate myself on everything twin related and that really opened my eyes. Interesting.

 

Absolutely FASCINATING!!!!!!!!!!!!!!!!!!!!!

PLEASE post some pics of the ultrasound. Plus, do you have literature or sites that have info on this??? Pls post them. Just amazing what seemingly impossible things CAN happen. I do NOT understand how this is possible but I also do not understand how chimeras are formed either. It's just INSANE! I guess the next step for your twins would have been a chimera formation??

PICS please! Congrats on your twins! So, the CVS came back one boy, one girl, correct? Genetically perfect?? Unreal!

I'm going to be checking this thread often cuz I'm amazed!

 

OMG, just read further on to see your reply on the chimera situation. Great minds think alike!

Wow! Thanx for posting that NOW PICS!

 

I saw part of a special once about this women being her own twin. She had two sets of DNA. Is that chimera? Was she the survivor of a vanishing twin with chimera, hence the two dna's?

 

Absolutely Fascinating!! Can't wait to see your story play out.

 

Where do you guys live? Do you think they'll write about your twins? :good:

 

hi everyone, thanks for the messages! we live in denver. our doc will be writing up a medical report on our situation due to how rare it is.

chimerism takes many forms and it is a fascinating aspect of biology and nature... basically yes, one person can have two DNA sequences and one of the ways is as you mention, absorbing a twin in utero and taking on that twin's DNA. our twins' DNA were already separate because they were two separate eggs, but now because they are sharing blood as identicals do, there is a chance that each twin's body will absorb the blood type of the other twin.

i have some ultrasound photos but you can't tell much from those that's any different from any twin ultrasound photo unless you're a doc trained in the subtleties of ultrasound readings and even then only the first ultrasound distinctly showed the wall and single chorion. what we're amazed at is how big my wife's belly is already, just 21 weeks into the pregnancy... she is as big as she was at 31 weeks with our first! it's getting hard for her to move around and pick up our 13 month old. she will most likely go on bed rest in another couple of months.

i will post with any new info and keep you all updated. thanks again for the welcome!

 

Just wanted to give you some friendly tips. Since I had TTTS I am aware of all the warnings. Sudden growth or weight gain can signify excess fluid. If it happened suddenly you should get it checked out. However it is normal to measure ahead in a twin pregnancy.

 

Hey, I don't care.. I MUST see pics!!!!!!!!!!!!!

Come on.. show us!!

 

Wow, fascinating! I understand your doctors testing for Turner's and other genetic abnormalities. Here's why (and I am sure you understand this; it's more for everyone else):

From Can Identical Twins Be Different Genders?

Welcome to Twinstuff! :welcome:

 

More....

Or, alternatively, the originally fertilized egg could have one extra X chromosome (47, XXY), which is called Klinefelter's syndrome. If the egg then split and one of the embryos subsequently lost a Y (46, XX), you would get boy/girl twins with the boy having Klinefelter's.

Here is a really fascinating article in the journal Nature!
Human genetics: Dual identities.
When I first read this article (years ago), it was free. Unfortunately, now, it is not.

Some interesting quotes from the article-
“Human chimaerism first came to light with the advent of blood typing - some people, it emerged, have more than one blood group.”

“Twin embryos often share a blood supply in the placenta, allowing blood stem cells to pass from one embryo and settle in the bone marrow of the other, seeding a lasting source of blood. As a result, as many as 8% of non-identical twin pairs have chimaeric blood. And given that most multiple conceptions that result in live births involve the loss of one twin early in pregnancy, there may also be significant numbers of blood chimaeras among single births.”

“True chimaeras, in which many tissues are affected, are thought to be very rare, and can form when non-identical twin embryos fuse shortly after fertilization.”

 

This is a brand new member. Leave 'em alone already.

 

Tsk Tsk. Not very nice. You and me have been through this before.. haven't we? Let's not do this again.

I don't need to justify myself to you.

To original poster: I was JOKING. I'm sure you wouldn't take me AS seriously as some do

Congrats on your twins I won't be checking back again. Thought I was having fun again and guess I'm NOT!

 

LOL, you are funny, and no, I do not take you seriously.
BTW - I am glad you edited your post.