Low Placenta at 21 Weeks

Luisa
At my last ultrasound the dr informed I have a low placenta, however specifically said its NOT praevia, just sitting low.  Didn't seem too concerned and said its likely to move up as I get farther along.  Just wondering how many of you had/have similar circumstances.  Vaginal birth is very important to me so I'm trying to gauge my risk for a c section.  Thanks!