Placenta Previa (low laying placenta)

This is my 3rd pregnancy. I have had vaginal birth with my first two kids with no complications or any type of worries. I am now 24 weeks  and was told that my sonogram that was done at 20 weeks showed the placenta still over my cervix. I am scared to find out if I have to have a c section. Have any of you other ladies had this happen and did the placenta move or did you eventually wind up having a c section??