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OK, sono techs, midwives, twin moms --

post #1 of 9
Thread Starter 
(I also posted this on the I'm Pregnant board)

Do you know if there are other clues besides gender that can indicate whether twins on ultrasound are identical or fraternal?

I don't want to know gender yet, but dh wants to know whether they are ID or frat... my perinatal doc asked if I wanted to know what she thought, after one sonogram... Since I've prayed for years for identical girls, I told her not yet, because I figured if she says fraternal, then they'd obviously be b/g and it would spoil the gender surprise. I can't imagine two little babies looking different enough on the sonogram to be able to tell whether they're identical or not?!? (ID can have two placentas, and two fraternal placentas can merge to look like one...) Can sonogram show whether same sex babies are identical or fraternal?
post #2 of 9
You won't neccesarily have b/g twins if they're fraternal. I have boy twins and they are most definitely NOT identical. I believe when they are fraternal they do not share the placenta or amniotic fluid and there is a membrane that separates the babies. In a monozygotic pregnancy, I believe they share the placenta and amniotic fluid (someone correct me if I'm wrong; I'm a bit sleep deprived right now! ) There are also cases where the twins do not share a placenta but are identical due to the time frame when the egg split. I'm really not sure how this works, but a friend was telling me about it when I was preggo. Apparently her sister had identical twin boys, but the doctors assured her they were fraternal because they had their own placentas etc. Turns out after a blood test/dna test that they were actually identical.
post #3 of 9
Originally Posted by Fleurette
There are also cases where the twins do not share a placenta but are identical due to the time frame when the egg split. I'm really not sure how this works, but a friend was telling me about it when I was preggo. Apparently her sister had identical twin boys, but the doctors assured her they were fraternal because they had their own placentas etc. Turns out after a blood test/dna test that they were actually identical.
This is what happened with my girls also. They each had their own placenta, chorion (the outer part of the sac) and amnion (the inner part of the sac). The ultrasound tech AND my OB told me that they were dizygotic (fraternal). I did reading on how twins are formed and found out that if the egg splits before day 3 after being fertilized that the twins will share nothing. This happens in 25-33% of the time with monozygotic twins. That's 1 in 4 pairs!!!! I told my OB that stat and he said he didn't realize the chances were that high. So, what we had to do was have their blood typed when they were born. If their blood type was different we would have known for sure they were fraternal. They had the same blood type so we had to have the DNA test done. Also, you CAN NOT go by looks alone. My girls looked nothing alike at birth but now look so much alike. Their DNA test came back that they are monozygotic (identical) twins.

To the OP....other then knowing FOR SURE that your babies are boy/girl there is no other way for the ultrasound tech to know if they are fraternal. She would be able to tell (without telling you the sex) if they were identical. The babies could be sharing the same chorion and/or amnion which definitely indicates monozygotic twins. However, you can't determine zygosity by the number of placentas. What looks like one placenta may actually be two that have fused together. So, you could take her comment two ways. Either your babies are boy/girl or she is guessing based on the fact that your twins share nothing. There are SO MANY techs that don't know that twins don't have to share something to be monozygotic. Did I make that clear as mud?

Also, as a side note, I took our DNA results to my OB's office as soon as I received them. I was so happy when he was very cool with being proved wrong and kept a copy of the results. He made it a point to inform his techs of their mistake and educate them!!
post #4 of 9
Assuming you haven't already had a test like amnio or cvs, in which case they *can* tell you if they are ID or frat with certainty, there is usually no way to know.

If they haven't already told you that the babies are monoamniotic or monochorionic, chances are they can't tell (unless, as you mention, they are b/g). If one or both of those structures is "mono," it means a higher-risk pregnancy (much higher with monoamniotic, slightly higher with monochorionic), but it also means that they are identical/monozygotic. But if you're seeing a perinatologist, you would have already gotten this information as a reason for special monitoring, etc. They wouldn't have thought to ask you if you wanted to know if they were ID, they just would have told you!

Many people don't find out if same-sex twins are dz or mz until years after their birth. You can do a simple mouth swab and send it off to a lab to have it analyzed to find out for sure.

GL to you for a healthy pregnancy!

post #5 of 9
my girls are fraternal as fraternal can be lol..they are different as night and day (one looks like me the other looks like their daddy)

but i had my first u/s at 11 weeks..and the tech there said when i asked her..'almost positive they are fraternal' she does 'twins clinic' as they call it at the hospital i delivered..and she saw many many woman with twins and anyhow..she was almost positive they were frat and they were. the girls each had their own placenta and sac..and a big thick membrane between them..plus i was on clomid and figured i released more than one egg
post #6 of 9
Your twins are DEFINITELY DZ if:
One is a boy and one is a girl

Your twins are DEFINITELY MZ if:
They share a sac
They definitely share one unfused placenta (which can be very hard to tell as sometimes DZ twins' placentas fuse--so really, unless they show signs of TTTS this is a maybe until they're born, and maybe even after that).

Otherwise, you'll have to get a genetic test to know for sure. MZ twins can have totally separate placentas. DZ twins can have a placenta that's nearly seamlessly fused, or fused enough that a doctor that's not used to twins can't tell.
post #7 of 9
My ID twin boys also had separate placenta, amniotic sacs and chorionic(though at birth they thought that there actually was only one placenta but then figured it may been due to fusion). It's also very hard to tel via U/S if there is one amniotic sac or not as the membrane is very thin. I think there is a window of a certain time frame (like between 11-13 weeks) where it's best senn on a U/S. THis is like pp have said best found out during an amnio test. THere are other tests but I wouldnt have them done unless there was a question of complete viability - these tests are things like shooting dye into the amniotic fluid and then taking it out from the other baby; if the fluid is coloured, well you know! This is done with an amnio but sometimes is done just to establish the number of sacs.

Anyway...off on a ramble sorry, was fascinated when I learned I was having tiwns (no fertility and no history of twins on any side of the family!) My OB had given me this little "chart" to help me when I was looking into how twins form.
When the zygote splits before the yolk sac is formed
each twin has his/her own placenta and is Dichorionic Diamniotic

When the zygote splits after the yolk sac is formed
twins share the placenta, but have own chorionic and amnionic sac they are Dichorionic Diamniotic-fused placenta

When the zygote splits a day or two later after yolk sac formation
twins share placenta and chorionic sac, but have their own amnionic sac - they are Monochorionic Diamniotic

When the zygote splits several days after yolk sac formation
twins share all three they are Monochorionic Monoamniotic

When the zygote splits after 12 days or more, then the twins are comjoined
post #8 of 9
ditto to that... throughout my pg, we had several level 2 u/s and each time someone would tell us something different... we knew early on that they were both boys (little winkies were VERY obvious... no amnio for us.) so it was anyone's guess as to what they were. they were in seperate sacs, had one fused placenta but look an awful lot alike. we just haven't had the extra $$$ for the DNA test. i wish i would have thought to had their blood typed at the hospital and they haven't had a reason since then to have any blood drawn. that would at least give me another clue! if your little ones are same-sex, i would just wait and have the DNA test done once they're born. that will tell you once and for all.
post #9 of 9
oh yea..ditto on the 'window' of 11-13 weeks..i hadmy first ultrasound at 11w and another at 13 weeks (and lots after that).but after 13 weeks it was harder to see the membrane..so had i not had the first u/s or the 2nd u/s when i did..i probably woudlnt have had any clue to anything about the girls..
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