Identical or fraternal??? Please help!

[Minoune79]

Ok, here's the story.  I found out I was having twins at 10 weeks through u/s (as it was a natural pregnancy).  The membrane between the two fetuses was very thin and hard to see.  See pic below.  The pic isn't the greatest as they gave me two of each baby instead of both on the same pic.  However, you can see Twin B on the left and part of Twin A on the right.  No membrane is visible on the pic even though there really is a very very thin one.

My OB/GYN told me she saw one placenta and thus we were expecting identical (mono) twins.  I have been seen by the hospital high-risk pregnancy dept every 2 weeks since then to ensure no TTS was happening.  Howevever, during my 16th week of pregnancy, I saw a new doc at the hospital who now says he thought he saw 2 placentas.  I saw him again today (at 21 weeks) and he's convinced there really is 2 and that they are fraternal.  I'm super confused as originally, they were telling me they were mono (due to one placenta and a very thin membrane), but now this other doctor comes along and tells me there is two placentas and the odds are 75% that they are fraternal.  I myself feel that they are identical due to the fact they the membrane between then is so thin (I have seen u/s pics of fraternal twins and the membrane is much much thicker than mine).  I'd really like to know your opinion on this.

Also, is it really possible to have 2 placentas, and a very thin membrane dividing them, making them fraternal?  Thanks for your input in advance :)

[lesliesara63]

From what I have been told a thin membrane usually means they are in the same sac. I know with my u/s at 7 & 9 weeks you could clearly see the shape of the sac & see that they were in one sac with a thin dividing membrane. No doctor would confirm that they were identical. It was only after the pathology report that it was confirmed that they had one placenta and not two that were fused.

[gozal]

That really is very confusing (and frustrating, right?)! From what my doctors told me, it is not possible to confirm DZ twins unless they are two different sexes (even then they could be identical, but that's very rare). Conversely, MZ twins CAN be confirmed if they share ANY membrane or a placenta. DZ twins do not share any membranes - maybe the u/s pics you have seen show DZ twins implanted close to one another so their chorions are close together? Of course, there are also MZ twins who are di-di with separate placentas, though the MFM doctor told me that is rare and mine are presumed fraternal. He said most MZ twins are monochorionic-diamniotic. Mono-mono are also rare. He also said that the best time to identify separate or shared placentas on u/s is before 12 weeks, and after that it is not very accurate. Based on my totally non-doctor-credentialed opinion and how my own u/s pics look, I'd guess yours are mono-di. HTH!

[Tigerchild]

Originally Posted by lesliesara63 

From what I have been told a thin membrane usually means they are in the same sac. I know with my u/s at 7 & 9 weeks you could clearly see the shape of the sac & see that they were in one sac with a thin dividing membrane. No doctor would confirm that they were identical. It was only after the pathology report that it was confirmed that they had one placenta and not two that were fused.

No, if they are in the same sac, there would be NO membrane, not even a thin one;  that is a very rare (and potentially dangerous) situation. 

[Tigerchild]

Originally Posted by Minoune79 

Also, is it really possible to have 2 placentas, and a very thin membrane dividing them, making them fraternal?  Thanks for your input in advance :)

Neither the placenta nor the membrane has *anything* to do with zygosity.  You can have DZ twins who appear to have one placenta (and it's later discovered that they did have separate ones that fused) and you can have MZ twins who implant across the uterus from one another and therefore have very distinct placentas and sacs. 

U/S does not diagnose zygosity.  Truly, only a genetic test and/or placenta pathology report can do that (and even then the latter may not be totally conclusive, esp. with 2 placentas).  Certain markers give clues to likely zygosity.  But unless you have the very rare occurance of mo-mo twins who have complications that are obviously due to being in the same sac or conjoined twins, you simply aren't going to know 100 percent in many cases what the zygosity is.  And u/s is an u/s and can get you a very good 'best guess'--but it's still a best guess except for very specific situations.

There are even conditions that cause complications similar to TTTS that can happen with twins who do not share placental connections!

[Minoune79]

What really upsets me is that because this 'new doctor' is writing di/di in my chart now (at 21 weeks) due to his theory, he has scheduled me to 3 week checkups now instead of my consistent 2 week checkups.  I have been seen every 2 weeks for the past 10 weeks, and now he decides they are di/di, so no TTTS is possible and thus 3 weeks is good.  I not only have a 'high-risk pregnancy' due to the twins.  I also have a shorter cervix, thus checking my cervix is crucial to ensure it stays closed.  I have done tons of research online and have also read that it is much easier to determine zygosity before 12 weeks.  So, I'm feeling like he's taking his theory a little too far.

[Minoune79]

Ya, I don't think so as the thin membrane between the two is very wispy - its like a small film floating in water.  I don't think chorion membranes do that.

[Red Pajama]

If you are uncomfortable with the 3 week time between appointments, tell the doctor. Ask for the 2 week interval to be kept.

[13pumpkins]

Originally Posted by Minoune79 

What really upsets me is that because this 'new doctor' is writing di/di in my chart now (at 21 weeks) due to his theory, he has scheduled me to 3 week checkups now instead of my consistent 2 week checkups.  I have been seen every 2 weeks for the past 10 weeks, and now he decides they are di/di, so no TTTS is possible and thus 3 weeks is good.  I not only have a 'high-risk pregnancy' due to the twins.  I also have a shorter cervix, thus checking my cervix is crucial to ensure it stays closed.  I have done tons of research online and have also read that it is much easier to determine zygosity before 12 weeks.  So, I'm feeling like he's taking his theory a little too far.

Zygosity is best determined by genetic testing for same gender babies.  The only U/S diagnosis of zygosity is when babies do not share a gender (faternal), cojoined twins (ID), and/or twins that share their amniotic sac (ID).  You are also correct about it being harder to determine zygosity after 12 weeks.  I am expecting triplets right now and there was a debate as two were implanted very close together.  Each have their own amniotic sac but it was debated (one OB said shared chorion one said separate) about the two closely implanted.  At my 16 week appointment, the placentas (whether it was 2 or 3) have fused into a larger placenta making it impossible to continue the debate!  Regardless, our OBs have selected to just watch them at a schedule that we are comfortable with (right now we go in every 3-4 weeks).

I think ultimately, it comes down to comfort.  If you do not feel comfortable with your new schedule, I would speak up.  Our trips (and me) are presenting very healthy so there is no reason for us to go in more often.  Moreover, as horrible as it sounds, there is little we can DO at this gestational age.  Howevever, my spouse and I are comfortable with our schedule.  I would discuss these concerns with an OB you feel more in tune with.  Afterall, he is providing YOU a service not the other way around.

[nd_deadhead]

Yep, the others are right - first of all, identical twins can have separate placentas, and it's impossible to tell on a scan if it is one placenta, or two fused. To me, the thin membrane suggests just an amnion separating them, and they share a chorion - that was the case with my twins. But in that case they would also share a placenta.

I would worry about a doctor that does not understand that idential twins can have separate placentas! What else doesn't he know about a twin pregnancy?

[ackerna]

If you twins share one sac - they are identical - no doubt as the only way this can happen is if the egg splits. 

There are 2 types of twins that share the same sac (outer membrane).  Monochorionic - monoamniotic (MOMO) and mono chorionic diamniotic.  My idential twins were the latter.  What this means - MOMO twins share the same outer sac (the chorionic sac AND share the same amniotic sac.  this is a very very high risk pregnancy - they first thought my twins were this way.  The second situation is where they share the same outer sac (chorionic sac) but have separate amniotic sacs.  This can be evidenced by seeing  a membrane between the twins that are sharing the one outer sac.  the membrane between my twins was very thin and even had holes - but the key was that it was there! 

If the twins are in separate outer sacs, then the only thing that can be determined for sure is if they are DZ (or fraternal twins) and that is only if they are different sexes.  Identical twins that split early in the process will also be in 2 separate sacs.

If the placenta appears to be one placenta - that can be deceiving as 2 placentas can fuse to look like one.  Further testing is required to determine this. 

[Minoune79]

Actually, its the other way around... I had seen 3 separate doctors at my 8, 10 and 12 weeks, all telling me that they suspected I had only one placenta.  Then, at 16 weeks, this new doctor makes a new theory stating he thinks there are two.  I agree with you Red Pajama and 13pumpkins.  I am seeing my OB/GYN next week, so I will let her know that I'm not happy about my monitoring frequency decreasing and to put a note in my chart about it.  I feel this doctor is going 'beyond' his role and getting into territory that doesn't really regard him - and only creates confusion and issues.  He should learn to do his job, check my babies developmental progress and my cervix and thats it.  Keep his theories to himself - not post them in my chart, and change everything!

[tink79]

My twin pregnancy was exactly the same as yours.  Just under 10 weeks, the membrane was barely visible, doc said identical, but as the pregnancy progressed, their sacs became more defined and we had two placentas and they were labeled fraternal for the rest based on the two sac, two placenta thing.  After birth, we had genetic testing and they are in fact, identical.

[Minoune79]

Originally Posted by tink79 

My twin pregnancy was exactly the same as yours.  Just under 10 weeks, the membrane was barely visible, doc said identical, but as the pregnancy progressed, their sacs became more defined and we had two placentas and they were labeled fraternal for the rest based on the two sac, two placenta thing.  After birth, we had genetic testing and they are in fact, identical.

That's very interesting!  So was there really 2 placentas at the end, or just one?

[~Adorkable~]

As another side note I had a DI/DI pregnancy and at every u/s I would ask about placenta locations, and was usually always told the same thing, that they were far apart from each other and one was top left towards my back and other was low of my right side. Totally separate 2 placentas. So it was a amusing surprise to me when I looked at them afterward and thought for a second that they took one away, they were infact completely fused and looked in everyday to be a single one, heck the two cords were less than 2 inches apart.

If my babies had not been different sexes I would have tested then for zigosity right away. Just goes to show how a very big thing can be seen wrong on u/s.

[tink79]

That's very interesting!  So was there really 2 placentas at the end, or just one?

Two placentas, but they were fused.