An ultrasound will tell you.
I couldn't tell... but at my 20wk scan and growth scan at 28wks the Tech said it was anterior.
I probably could have guessed because all the babies movements are very dull in the front and strong everywhere else!
The midwife may be able to tell from doppler?
I didn't know with my first, but at my 20week scan for my second baby they said its to left and abit in front but not in the way.. Think you could ask your midwife cause I think they feel for it or ask at your next scan X