How can doctors tell if you are having identical twins from an ultrasound?


How can doctors tell if you are having identical twins from an ultrasound?

In: 98

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).


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.