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Fraternal vs. Identical

post #1 of 51
Thread Starter 
I'll apologize now because I am still not up on all the lingo for twins refering to sharing a placenta, or amniotic sac and such.

Anyway, my RE said that my twins are fraternal at the exit interview when I was 8 weeks. Can they diagnose that at that point? I thought it required an ultrasound betwee 10 and 12 weeks to tell for sure? If it matters, we were able to see two embryonic sacs, each with it's own embryo and yolk sac.

Also, if you know of a good link to explanation of MZ vs. DZ and such, I'd appreciate it. TIA!
post #2 of 51
Congratulations on your twins!

Twins who each have their own placenta can be MZ (identical) or DZ (fraternal). If MZ twins split really early, they don't share anything. If they split a bit later, they share a placenta. If they split later yet (like my girls) they even share their amniotic sac. If they split later yet, they're conjoined.
DZ twins always have their own placenta, though the placentas can squish together (I forget the medical term!) which gives the illusion that there's just one.

So just seeing two placentas doesn't mean they're DZ. I think if you get a very early ultrasound, sometimes they can tell? But otherwise, you either have to wait until you can tell gender (boy/girl twins are always fraternal (okay, with a one in like fifty trillion chromosomal disorder exception)) or until they're born and you can blood type/DNA test them.

Wikipedia's page on twins actually has a pretty good breakdown of DZ/MZ definitions, with illustrations.
post #3 of 51
:

There is a very common misconception that two placentas and two sacs means fraternal. That's just not the case (and it always shocks me when medical personnel don't know the basics of twinning). Separate sacs and placentas only mean less potential complications. It's one of those rule in things. If they have one placenta they are for sure identical. If they have two they might be fraternal or they might be identical.

Did you have any sort of amnio done? They could tell for sure by that but otherwise I'd say you're still up in the air here.
post #4 of 51
if you had ivf maybe they could tell? that's the only way i can guess they would know for sure.
post #5 of 51
Thread Starter 
Quote:
Originally Posted by aja-belly View Post
if you had ivf maybe they could tell? that's the only way i can guess they would know for sure.
Yes, we did IVF and they transferred two embryos, so it's very likely they are fraternal. However, I thought there was still a chance of one splitting and the other not taking, which would make them identical. Maybe it is due to the early u/s. The u/s started at 5 weeks, so if those show, then he would know. I'll just confirm with my ob when we meet next week.
post #6 of 51
If it's boy/girl you'll know for sure too.....
post #7 of 51
i was just thinking maybe if they split at that point (after ivf) maybe they would have to be in the same sac? i'm no expert, but if that was true then that might be how he would know.

of course the woman who did our first u/s said they weren't identical cause they were in seperate sacs, so it's also possible that your doc was just wrong.
post #8 of 51
Quote:
Originally Posted by Intertwined View Post

There is a very common misconception that two placentas and two sacs means fraternal. That's just not the case (and it always shocks me when medical personnel don't know the basics of twinning).
:

I have a friend who had 3 implanted and one split, so she ended up with quads. So, although it's likely that they're DZ, it's possible that only one took and then it split.

The only way to guarantee DZ with an u/s is if they're b/g twins.

But like a pp said, seeing 2 placentas and 2 sacs means less chance of complications!
post #9 of 51
I was told multiple times during my pregnancy that my boys were fraternal and they are identical (we had them tested and it is pretty obvious too ). They had their own sac and placentas and I guess that is why they told me that. If they could tell you had 1 girl and 1 boy then that is pretty obvious but other than that it is pretty hard to tell. I would not really go by what they say unless they are b/g twins.
post #10 of 51
I have di/di identical twins, meaning they did not share a placenta or a sac. According to the doctors, they were fraternal. I was told that throughout my pregnancy, and heard it at the first ultrasound at 12 weeks. I did some research and found that there was a 25% chance they could be ID, so I figured I would wait until they were born to find out. After they were born, they looked exactly alike, both had blonde hair and blue eyes, and the same blood type. At 4 months I had them DNA tested and sure enough, ID.

Soon after their birth I was billed for a placenta check, I called my OB and asked if they tested the placenta to see if they were frat or ID, he said "there was no need, they are fraternal". After I had them tested and saw him again I told him that he needs to stop telling everyone women pregnant with twins that there is not such a thing as ID di/di twins. He said that they are so rare that no one bothers to mention it
post #11 of 51
I was told at my 20 week u/s that you can only tell if they are ID or not during first tri. The tech said they count the number of layers in between the sacs. It's something like if there are fewer than three layers, they are ID and more than three and they are frat.

I don't know, that is what I was told anyway.
post #12 of 51
I was told fraternal because they had their own sacs and placenta area had that delta sign that looked like 2 placentas merged together. OB said well then they're fraternal. At birth, it was a shared placenta, and NOPE they are definitely identical thanks to DNA testing.
post #13 of 51
I'm shocked and disgusted at the number of medical "professionals" who assume that two sacs = two eggs!! Anyone dealing with women pregnant with twins should know these things. Grrr!

vanauken explained it very well. The earlier an egg splits, the fewer (if any) membranes monozygotic (identical) twins will share. Our twins had separate amnions (thankfully), but shared a chorian (outer sac) and placenta. Because the amnion is very thin, and hardly even shows up on ultrasound, we suspected our babies were identical, even before they were born.

The membranes were examined at birth to confirm that they did, in fact, share a chorion. But if they had split earlier, they could have had separate everything and still be identical. So examining the membranes can confirm identical twins, but cannot rule it out.

The only way for sure to tell if twins are fraternal on ultrasound is if they are boy/girl.
post #14 of 51
Quote:
Originally Posted by shukr View Post
If it's boy/girl you'll know for sure too.....
I used to be on a multiples forum where people would go up-in-arms over the above. SOMEONE had a set of twins in which one child had Turner's Syndrome. So she had a set of twins that were identical but were essentially boy/girl genders.

So many people in this group always pointed out to new members that boy/girl twins CAN be identical. It used to drive me crazy. They're actually boy/boy with one having a chromosomal abnormality and there are only a handful of twins worldwide who can say that.
post #15 of 51
Our boys had two sacs and one placenta throughout most of the pregnancy. Everyone was convinced that they were identical and when at 36 weeks Raphi didn't grow and Danny did, they decided that the difference in size was too big and given that there was one placenta, we decided that I needed to deliver. The OB who delivered them examined the placenta for almost ten minutes before pronouncing them identical, and they did look very much alike until they were about three months old. Then, the just grew to look like themselves. They have the same face, but different features and now just look like siblings. We didn't feel the need to do DNA testing. So sometimes, the techs, doctors and "professionals" can be wrong.
post #16 of 51
Shuli, obvously it's too late now, but if a pathologist had examined the membranes after you delivered, they could have determined if there was, in fact, just one placenta, or if the two placentas were fused together (which can happen with fraternals or identicals). One placenta means identical for sure; fused placentas could be either idential or fraternal.
post #17 of 51
Quote:
Originally Posted by Shuli View Post
Our boys had two sacs and one placenta throughout most of the pregnancy. Everyone was convinced that they were identical and when at 36 weeks Raphi didn't grow and Danny did, they decided that the difference in size was too big and given that there was one placenta, we decided that I needed to deliver. The OB who delivered them examined the placenta for almost ten minutes before pronouncing them identical, and they did look very much alike until they were about three months old. Then, the just grew to look like themselves. They have the same face, but different features and now just look like siblings. We didn't feel the need to do DNA testing. So sometimes, the techs, doctors and "professionals" can be wrong.
I haven't seen your twins but from what you're saying I'm throwing in a vote for MZ. Your description just sounds SO much like all my other MZ-in-denial MoM friends.
post #18 of 51
My identicals have different shaped heads, it throws people off. I think in my case, their in utero environments were very different and that affected how they grew but I know their identical without genetic testing.

And I've seen non twin sibblings that looked an awful lot a alike.
post #19 of 51
Now you all have got me really curious to confirm if our twins are fraternal!! I had an ultrasound at 5 weeks, 6 weeks, and again at around 8 weeks and the doctor told us they were fraternal- two sacs and two placentas.

EVERYONE thinks they are identical. They both have blue eyes and blonde hair. They look very much alike except for the shape of their faces. They also are about 1-2 pounds different in weight. Most people I've talked to with ID twins are exactly the same weight.
Our older three boys all look SO different! So it does surprise us that these two look so much alike. Has anyone else had this experience? Would you do a DNA test?
post #20 of 51
Quote:
Originally Posted by 2+twins View Post
I haven't seen your twins but from what you're saying I'm throwing in a vote for MZ. Your description just sounds SO much like all my other MZ-in-denial MoM friends.
2+twins strikes again!

You just like to accuse everyone else's twins of being identical because you're obviously in denial about your own boys' MZ status.

laughup
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