i'm 25 wks and i went to the doc today and the gp gave me the results of my 21 wk ultrasound and said i have to go for a follow up ultrasound at approx 34 wks due to my placenta being posterior and only 2.5 cm away from my cervix. she said its supposed to be a bit more away (i can't remember how far she said) and hopefully it will have moved by the next scan. is this at all dangerous., and has anyone else had this and it hasn't moved up.?