How can doctors tell if you are having identical twins from an ultrasound?
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At a 12-week scan. they should be able to tell whether the babies share a placenta (meaning they’re identical) or if they have 2 separate placentas (meaning they can be identical or not).
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I was also told once that rarely two placentas can fuse into one early enough as well.
Can anyone confirm?
I was always under the impression that the only 100% way to tell was a DNA test.
There are some ways to tell, but some times we cannot. Here are the three possibilities:
A) If one is a boy and the other is a girl, we know they are not identical.
B) If they are monochorionic, that is, if they share the same placenta, we know they are identical.
C) However if they are the same sex and are dichorionic (two placentas) they could be either fraternal or identical.
Identical twins can have separate placentas, share a placenta, share an amniotic sac, or even be conjoined, depending on when the twins separate. If they share an amniotic sac (monoamniotic) or if they are conjoined, they always share a placenta. That’s why I didn’t include those possibilities separately above.
On the ultrasound, they look for a little line circling the fetuses. That’s the placenta. If the line goes between the two fetuses, there’s two placentas and they could be either identical or not. But, if they just see one circle with no line between, the fetuses are sharing one placenta, and in that case they are identical twins.
They can tell from how many placentas and sacs these help determine the type of twins you have. I had a 9 week scan and they were able to tell me and the husband we had identical twins in separate sacs
Identical twins happen when a single fertilised egg splits into two babies– they will share a baby sac.
Fraternal twins happen when two separate sperm cells fertilize two released egg cells, creating 2 separate baby sacs growing side by side.
This happens largely based on which parent is carrying the “twin” gene. If the mother’s parent was a twin, there’s a chance that she releases two mature eggs every month, and fraternal twins are likely. If the twin gene is running on the father’s side, his swimmers could be set to split once they reach their target, creating identical twins. (This explanation is very basic and there are exceptions to everything, but I studied a lot about twins because my dad is one.)
Depending on the day they split, there are a few options but most identical twins share the placenta and the outermost layer of the sac, but have their own inner sacs (mono di twins). On ultrasound they can see the differences between these sac layers versus fraternal twins. Some identical twins share the inner sac as well, which is a dangerous situation and I can remember the ultrasound techs looking carefully for the membrane that separated them to confirm that wasn’t our case.
At 4 weeks a vaginal ultrasound showed we were having twins. It was fairly easy to see the sac. At six weeks we could see an additional sac. It is fairly easy to find and see. At this point you could see the embryo inside the sac. Really cool. This was 25+ years ago so it is probably better now.
In an early ultrasound they can probably tell from the yolk sac. The main sac looks like a cavity in the ultrasound. If there is one sac with two embryos it could be identical twins. There is only one yolk for identical twins because there was only one egg. Not sure of this is reliable but it is an example the kinds of images they get and the clues they go by.
Someone I know had an ivf implantation of one egg and had twins so obviously they were from one egg when the ultrasound showed two.
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