If it hasn't been mentioned, then it's likely there are no concerns :) Might be noted on your notes from your 20 week scan if you have a copy of those x
If on your scan reports it says the placenta site will either be Anterior (front) or posterior (back). It is only low lying if they have put the words "extending to and/or covering os" it will also have in bold further down the report "your name, advised of low lying placenta if bleeding occurs call triage and will list your triage number"
It should say on your scan notes. ☺️
They told me mine at my 20 week anatomy scan. It’s also on the report that they gave me. On mine it says posterior placenta.