Don't think turning in your sleep helps though :/ I've a reverse problem. I'm a light sleeper and I turn a lot in my sleep, since I tend to wake up when my husband moves.
I've also been active throughout my pregnancy; I swam, did pregnancy-friendly circuit / strength training, and yoga. None of which changed my baby's position. She has been facing my spine for awhile now and I think babies will only turn when they want to. Mine turned to a better position for measurements almost at the end of the scan and the sonographer got me to measure a second time so she could get better measurements.
Also, like you mentioned, it's harder to get good measurements when baby's back is against our belly. So don't worry too much if the measurements turn out to be a bit off! It happened for me and it was okay after I repeated the scan 2 weeks later and her position was better.
Anonymous