Hello!
I've just been through the exact same thing!
Had my 20 scan last week where 2 cysts were found in the lo's brain.
The sonographer was useless at the time and got us really worried, said he could really not say anything more about it and that we should take it one step at a time (!) I was referred to University College London Hospital yesterday and had another detailed scan where no other markers or abnormalities were found.
The sonographer at UCLH was extremely reassuring from the start. She said that it's common and normal, most of the time they go at around 24, 28 or 32 weeks, sometimes the baby is born and the cysts are still there, there is no impact whatsoever on the baby's brain or development.
She also said that usually, and more and more, if this is the only marker found you do not get referred as it is considered normal.
If you really want you can have an amnio to check the chromosomes but there is a risk of miscarriage and it is so common that we decided it really wasn't worth the risk.
I read a few posts where women had more than one soft marker, had lods of scans and saw them disappear one by one or get better or just be "one of those things" and still had healthy babies at the end of it.
I have been through hell the whole week after they found the cysts and before the scan yesterday and got really depressed about it. Now I feel 100% reassured and we won't go for another scan to check the progress, it is not needed.
One of the things they wrote on the report is: "The risk of Trisomy21 from the screening test was low (1 in 3000) and I have explained that as an isolated marker this finding does not change that risk. The parents understand that chormosomal abnormality can only be excluded by invasive testing and they wish to avoid this in view of the risk of miscarriage."
Everybody was telling me not to worry and that it was going to be fine, yet I couldn't stop myself from non-stop crying.
You can move on and worry about something else, that's what I did ;)