My ultrasound report at 19 weeks said exactly the same as yours, and my obs said that they'd do another ultrasound somewhere between 34-36 weeks and not to worry as in most cases it moves up. My obs also said that if the head had engaged that all would be fine for a natural birth. I'm trying not to think too hard about, but know that I just want what is safest for my baby's arrival. Good luck with the next scan!