anyone has mono/di twins that are fraternal?

nghithy · August 2012

I know 60-70% mono/di twins are identical with exception of a few where the placenta fused together. Anyone in that situation?

adoubleu12 · August 2012

Technically, if the placenta's are fused together, they are still two placentas which means it is considered di/di. All mono/di twins are identical.

macchiatto · August 2012

I think you might have your stats confused. 1 in 3 sets of identical twins is di/di and the rest are mo/di or mo/mo. I had always heard it's impossible for mo/di twins to be fraternal, though I think someone posted recently that it happened to them. Very rare though.

I was told at birth that my boys had one shared placenta, but they are clearly fraternal and I remembered the u/s tech telling me at my 12w ultrasound that they were di/di. (Though really, the drs never talked about that.) They weren't mo/di; their placentas fused.

Mrs. Alice · August 2012

nghithy:
I know 60-70% mono/di twins are identical with exception of a few where the placenta fused together. Anyone in that situation?

I think you mean 60-70% of di/di twins are fraternal? I agree a fused placenta doesn't equal mono/di either, they are still di/di. I don't think it's possible for mono/di twins to be anything but identical.

Rynleigh · August 2012

There are two ways that you could be *diagnosed* as mo/di and have fraternals:

Most common, the placentas fuse early, before you ever have an ultrasound. If the placentas are so merged by the time you have an imaging scan, it can *look* like mo/di, but it is technically just a di/di fusion.

The most rare scenario occurs when two separate fertilized eggs fuse during the zygote or blastocyst stage. Very rare, but possible. It's hypothesized to be the one scenario in which fraternal twins can suffer from TTTS, because connecting blood vessels in a placenta typically cannot develop in a fused placenta - but can develop if the blastocysts fuse before they implant, creating one single placenta

Again, the second scenario is extremely rare and relatively unheard of.

JenLC99 · August 2012

My twins are di/di fraternal but the placentas did fuse in late pregnancy. If they had both been the same gender and if we had not seen two separate placentas early on, we would not have known if they were identical or fraternal without genetic testing.

rinascita · August 2012

Rynleigh:
There are two ways that you could be *diagnosed* as mo/di and have fraternals:
Most common, the placentas fuse early, before you ever have an ultrasound. If the placentas are so merged by the time you have an imaging scan, it can *look* like mo/di, but it is technically just a di/di fusion.
The most rare scenario occurs when two separate fertilized eggs fuse during the zygote or blastocyst stage. Very rare, but possible. It's hypothesized to be the one scenario in which fraternal twins can suffer from TTTS, because connecting blood vessels in a placenta typically cannot develop in a fused placenta - but can develop if the blastocysts fuse before they implant, creating one single placenta
Again, the second scenario is extremely rare and relatively unheard of.

Yes Exactly this.

My MFM *thinks* my twins are Mo/Di but he said he can't be 100% sure b/c they could be Di/Di and their placentas fused based on his review of my 13w,2d u/s. It's like a puzzle he said, more and more pieces (e.g., are they the same sex) will come about throughout my pregnancy but we may never know 100% until they are born.

Most people don't know that you won't know if your twins are identical or fraternal 100% until they are born, unless they are Mo/Mo or b/g twins.

macchiatto · August 2012

Rynleigh:
There are two ways that you could be *diagnosed* as mo/di and have fraternals:
Most common, the placentas fuse early, before you ever have an ultrasound. If the placentas are so merged by the time you have an imaging scan, it can *look* like mo/di, but it is technically just a di/di fusion.
The most rare scenario occurs when two separate fertilized eggs fuse during the zygote or blastocyst stage. Very rare, but possible. It's hypothesized to be the one scenario in which fraternal twins can suffer from TTTS, because connecting blood vessels in a placenta typically cannot develop in a fused placenta - but can develop if the blastocysts fuse before they implant, creating one single placenta
Again, the second scenario is extremely rare and relatively unheard of.

Thanks for the thorough explanation! Am I remembering wrong though or didn't someone just post on here relatively recently that her di/di twins had TTTS? Definitely rare as I've been on twin boards for 4 years and it was the first time I'd ever heard of that.

ColleenS629 · August 2012

adoubleu12:
Technically, if the placenta's are fused together, they are still two placentas which means it is considered di/di. All mono/di twins are identical.

This. My boys' placentas fused together but it was clear in the beginning that they were separate. They didn't go from di/di to mo/di when their placentas fused. They were still di/di.

kiwi443 · August 2012

macchiatto:
Rynleigh:

There are two ways that you could be *diagnosed* as mo/di and have fraternals:

Most common, the placentas fuse early, before you ever have an ultrasound. If the placentas are so merged by the time you have an imaging scan, it can *look* like mo/di, but it is technically just a di/di fusion.

The most rare scenario occurs when two separate fertilized eggs fuse during the zygote or blastocyst stage. Very rare, but possible. It's hypothesized to be the one scenario in which fraternal twins can suffer from TTTS, because connecting blood vessels in a placenta typically cannot develop in a fused placenta - but can develop if the blastocysts fuse before they implant, creating one single placenta

Again, the second scenario is extremely rare and relatively unheard of.

Thanks for the thorough explanation! Am I remembering wrong though or didn't someone just post on here relatively recently that her di/di twins had TTTS? Definitely rare as I've been on twin boards for 4 years and it was the first time I'd ever heard of that.

Yes, someone here recently had boy/girl twins that were something like 4 lbs. apart at birth. The drs determined that it was a case of di/di TTTS. Her screen name is slipping my mind at the moment.

Rynleigh, I also appreciate your explanation, I didn't understand how it was possible before.

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