Cannot remember exact measurements Sorry.
I do remember reading somewhere that it is thought between 18 and 22 weeks the ventricle measurements can be large and then they can go down again to a normal size.
Could you contact someone at the RCH to see what they thought?
My tertiary scan was at RWH and they brought a pead over to consult me just in case the measurements were bigger than the 20 weeks scan.


I tell you what... everything is a soft marker for downs these days :S
My daughter who I had last year, had a 2 vesselled umbilical cord, which was a "soft marker for downs".
She showed no other markers, so they just kept an eye on her via u/s for the remainder of my pregnancy and she also was perfectly fine.

If they didn't mention any other markers, then you should be pretty positive. Usually they will search closely for other things associated (like a lack of a nasal bone).

If you feel everything is ok, then I'm sure it is. I knew both times my kids were 100% healthy. I just knew it.

All the best and I hope that someone can give you something helpful information wise.