Question on identical versus fraternal

Jen0204

My OBGYN had told me that I'm pregnant with identical twins - mo-di.  The way I understood it was that since they are in one placenta but with a membrane between them they are identical.  However, when I went to my MFM for my first-tri screening a couple of weeks ago he said that he thinks they could be fraternal.  He said that over the next couple of months they'll try to make that determination since identical twins have a lot more complications then fraternal.

My question is, why would it matter if they're fraternal vs. identical?  No matter what they are, they're still only in one placenta with two sacs.  Does what we call them really matter?  And is it odd that my OB was certain that they're identical and the MFM thought otherwise?

pea-kay

If they share one placenta, they're identical. No question. I'm not sure why your MFM is questioning it. Did he see the images from your first u/s? My MFM didn't, so he didn't know that mine were mo/tri, so that might be the case with yours.

In any case, sharing a placenta is higher risk than not. There are possible complications like TTTS. So yes, you need to be watched more closely because of that.

Mrs. Alice

It wouldn't really matter if they are identical or fraternal.  What matters as far as how your pregnancy is monitored, is the number of placentas and if they are in separate amniotic sacs.  Just to correct, they are not in the placenta.  They are in the gestational sac also called the chorion.  If they have one placenta and two sacs, they are always identical, so I'm not quite understanding what your MFM told you.  In some cases the placentas fuse together, making it look like one. 

Jen0204

That's what I thought, and I said to him that I thought that one placenta meant that they were identical, but he said that since they are in 2 amniotic sacs (since they're separated by a membrane) that they could be fraternal.  I also know from reading here that you can't always tell for sure without getting a DNA test after they're born, so it seemed odd to me that he was placing such an importance on determining that they are to decide if I need to keep seeing him versus just watching me closely since they share a placenta.

I guess I should break it to DH that there's really no chance we'll have a boy and a girl   He got his hopes up for that after the MFM said he thought they could be fraternal.

adoubleu12

Maybe he is referring to them being di/di but their placentas fused together?  I remember my OB saying something about that when she was explaining the types of twinning to me.. 

tmbuchmann

This conversation hurts my head (not sure why) maybe the link to the diagram would be good here!

pea-kay

Let me put this plainly, so there is no confusion.

IF they share ONE placenta, they are IDENTICAL. No matter how many amniotic sacs are involved.

If they each have their own (which is not the case for you, it has already been established by your OB/GYN that they are sharing a placenta) they MAY be identical, but are probably fraternal. 

zsvendsen

I have to admit that until embarrassingly recently, I didn't understand that a placenta didn't encircle the baby. Once I figured that little bit of basic anatomy out, everything twin-related started to make a LOT more sense.

I also don't know why your MFM wouldn't understand, unless s/he does suspect that the placentas fused and just didn't say so.

adoubleu12

pea-kay:

Let me put this plainly, so there is no confusion.

IF they share ONE placenta, they are IDENTICAL. No matter how many amniotic sacs are involved.

If they each have their own (which is not the case for you, it has already been established by your OB/GYN that they are sharing a placenta) they MAY be identical, but are probably fraternal. 

So you are saying di/di placentas can not fuse together?  Or are you saying if they fuse together they are still two placentas? 

pea-kay

here you go:

 

 

 

 

adoubleu12

pea-kay:

here you go:

 

 

 

 

Yes, I have seen the diagrams.  But it doesn't answer my question.  Sorry if I am sounding stupid, I haven't had my coffee. 

pea-kay

Allisonb17:

pea-kay:

Let me put this plainly, so there is no confusion.

IF they share ONE placenta, they are IDENTICAL. No matter how many amniotic sacs are involved.

If they each have their own (which is not the case for you, it has already been established by your OB/GYN that they are sharing a placenta) they MAY be identical, but are probably fraternal. 

So you are saying di/di placentas can not fuse together?  Or are you saying if they fuse together they are still two placentas? 

Even if they fuse, they're still two placentas. And they don't fuse that early on. She's only 14 weeks now, so I'm guessing her first u/s was a while back, when it's easy to tell how many placentas there are, and before they're squished enough to fuse.

adoubleu12

pea-kay:

Allisonb17:

pea-kay:

Let me put this plainly, so there is no confusion.

IF they share ONE placenta, they are IDENTICAL. No matter how many amniotic sacs are involved.

If they each have their own (which is not the case for you, it has already been established by your OB/GYN that they are sharing a placenta) they MAY be identical, but are probably fraternal. 

So you are saying di/di placentas can not fuse together?  Or are you saying if they fuse together they are still two placentas? 

Even if they fuse, they're still two placentas. And they don't fuse that early on. She's only 14 weeks now, so I'm guessing her first u/s was a while back, when it's easy to tell how many placentas there are, and before they're squished enough to fuse.

Okay.  Thanks for clearing that up for me!     

Jen0204

I don't think that there is any talk of there being 2 fused placentas, at least not that has been mentioned to me.  They've always seen one placenta with a thin membrane.  These are my 8w4d and 12w2d ultrasounds:

 

 

2shihtzus

At the risk of looking like a complete moron, I am kind of confusednow.  Based on what I have learned and seen here, I always thought that my ultrasound looked like a mono/di ultrasound (and I was treated as mono/di during my pregnancy).  But, after my boys were born, they tested the placentas and it turns out that they were 2 that had fused together.  I don't know why but I have always assumed that the fusing of the placentas happens early on which is why (I thought) my ultrasound looked mono/di.

Here is my 8 week ultrasound when we found out we were having twins, am I wrong thinking this looks like a mono/di ultraound?

Jen0204

Oh boy, it seems like my question has confused some people.  Sorry!  I'm just going to try to push for my babies to be watched closely in case TTTS becomes an issue, regardless of what my MFM "decides" they are, hope the babies are both healthy, and not worry about whether they're fraternal or identical until they get here.

pea-kay

2shihtzus:

At the risk of looking like a complete moron, I am kind of confusednow.  Based on what I have learned and seen here, I always thought that my ultrasound looked like a mono/di ultrasound (and I was treated as mono/di during my pregnancy).  But, after my boys were born, they tested the placentas and it turns out that they were 2 that had fused together.  I don't know why but I have always assumed that the fusing of the placentas happens early on which is why (I thought) my ultrasound looked mono/di.

Here is my 8 week ultrasound when we found out we were having twins, am I wrong thinking this looks like a mono/di ultraound?

You know, I don't put a whole lot of stock in the testing of the placenta. We had testing done on mine, and they couldn't conclusively say that it was just one placenta. Yours are quite obviously mo/di. As are OP's. 

Man, I should be an OB/GYN/MFM. hee!

Jen0204

pea-kay:

You know, I don't put a whole lot of stock in the testing of the placenta. We had testing done on mine, and they couldn't conclusively say that it was just one placenta. Yours are quite obviously mo/di. As are OP's. 

Man, I should be an OB/GYN/MFM. hee!

Too bad I can't send my co-pays your way - you've given me more information than either of my doctors!

2shihtzus

pea-kay:

2shihtzus:

At the risk of looking like a complete moron, I am kind of confusednow.  Based on what I have learned and seen here, I always thought that my ultrasound looked like a mono/di ultrasound (and I was treated as mono/di during my pregnancy).  But, after my boys were born, they tested the placentas and it turns out that they were 2 that had fused together.  I don't know why but I have always assumed that the fusing of the placentas happens early on which is why (I thought) my ultrasound looked mono/di.

Here is my 8 week ultrasound when we found out we were having twins, am I wrong thinking this looks like a mono/di ultraound?

You know, I don't put a whole lot of stock in the testing of the placenta. We had testing done on mine, and they couldn't conclusively say that it was just one placenta. Yours are quite obviously mo/di. As are OP's. 

Man, I should be an OB/GYN/MFM. hee!

Interesting!  I guess it doesn't matter now anyway but I was just curious.  Thanks!  (and yes, you should totally be an MFM or like some kind of patient advocate that explains everything to parents right when they find out they are having multiples.  I loved my MFM but you definitely make me understand things way better than she did, she never even made me a diagram! )

2shihtzus

Jen0204:

Oh boy, it seems like my question has confused some people.  Sorry!  I'm just going to try to push for my babies to be watched closely in case TTTS becomes an issue, regardless of what my MFM "decides" they are, hope the babies are both healthy, and not worry about whether they're fraternal or identical until they get here.

Don't be sorry!  My boys are 16 months old and I still get a little confused by all of this sometimes, it's a lot to take in and understand (especially when a lot of the time, you are still trying to take in the fact that you are having more than 1!)

pea-kay

2shihtzus:

Jen0204:

Oh boy, it seems like my question has confused some people.  Sorry!  I'm just going to try to push for my babies to be watched closely in case TTTS becomes an issue, regardless of what my MFM "decides" they are, hope the babies are both healthy, and not worry about whether they're fraternal or identical until they get here.

Don't be sorry!  My boys are 16 months old and I still get a little confused by all of this sometimes, it's a lot to take in and understand (especially when a lot of the time, you are still trying to take in the fact that you are having more than 1!)

Ditto to this! I knew NOTHING when I was pregnant. We didnt know they were ID until they were DNA tested at 3 months old. And it is completely obvious now that I look at my ultrasounds. But my doctors weren't terribly well-informed either. I did a lot of reading and research (because it's fascinating) after the boys were born. I spent my pregnancy in a haze. :P

kmb585

As our resident expert on this board says if: ONE placenta + 2 amniotic sacs = identical (no questions about it!)

That is very strange to me that your MFM would question if they are identical or not, they are supposed to be the experts in this.  I would definitely ask for clarification.

In my case my little guys are di/di - very easy to tell as at first u/s (~ 6-7 weeks) you could see 2 distinctly seperate circles (the moment the Dr. put the wand on I said OMG it's twins" before she even said anything).  As time has gone along it has been harder to differentiate the two placentas as they are both anterior and may have seemed to fuse ~ 18-20 weeks, but they can tell where there is a divider among the two.  So no matter if it fuses or not, once confirmed 2 placentas there is always 2 placentas.

An MFM that I saw with a previous multiple pregnancy that I unfortunately miscarried explained it to me like this:

If one egg is fertilized and it splits btwn day 0-3 after fertilization, they will likely be di/di but still "monozygotic" (the eggs splits early enough that they form their own placenta cells - thus why there is a 1:9% chance that di/di twins of same gender are ID); if the egg splits btwn day ~3-7'ish after fertilization they are mo/di (thus sharing a placenta but each have their own amniotic sac); If the spilt is btwn day 7 or 8 - day 11 after fertilization they are mo/mo twins (which is very risky as they both share placenta and same amniotic sac thus cord entaglement, etc can become serious issue); and last but not least if the egg splits really late 11+ days after fertilzation then you end up w/ conjoined twins (which is very rare and of course comes w/ it's own complications.

Which ever the scenario I hope you are able to get your questions answered. And to add that yes if they are ID, your husband will have to be prepared to know that they will definitely not be boy/girl twins.  (I mention this b/c w/ my miscarriage they were spontaneous ID triplets, however DH always thought there was a chance at least one could be a girl, to which I told him "ID means ID everywhere, they will all be the same sex" )

Jen0204

It's shocking to me how many people I've told that they're identical (before I met with the MFM) and then I'll get asked "so are you hoping for a boy and a girl?".  Uh, do you not understand what the word "identical" means? 

tmbuchmann

Jen0204:

It's shocking to me how many people I've told that they're identical (before I met with the MFM) and then I'll get asked "so are you hoping for a boy and a girl?".  Uh, do you not understand what the word "identical" means? 

Most people don't know what that means. I'm always explaining it, well sometimes I don't.