i had it with both my preg. With DD i was told it was low at 18weeks and had a scan at 30 weeks and it had moved and i had a VB with her. This preg i was told it was low at 19 weeks it was 1.4cm away from the cervix and i was told it had to be atleast 3cm for them to give the ok. they r not givin me another scan till 34 weeks this time and i was told there may be slight bleeding as it stretched up and that it is more likly that it will move. i read heaps about it as well and read that it can be completly covering the cervix and still move so that gave me alot of hope. dont stres until u have ur last ultrasound. With DD they didnt tell me that it was likly to move just that they would check it again later but that low means csect so i was freakin out the whole tiem then when i had my last ultrasound the ultrasound lady said oh this is a common thing you should of been told it would move.