Placenta position changed 21 weeks ,very concerned pls advise

[Hanah77]

Hi
My brief history is that I had 3 2nd trimester miscarriages.now I am 21 weeks pregnant and quite worried . With my history I am being offered regular scans every two weeks.i had low lying placenta to start with but after 18 weeks it was not low anymore. On my anomaly scan last week she wrote it as placenta site is anterior and high.
Now for the past two days I am having uti and feeling pressure down there so today went for a scan again . In today's report she wrote placenta site anterior low.
Now I am very concerned that how can placenta come low after being high. Do you think that this is a sign of preterm labour starting.please reply with your knowledge

I would have thought one of them was wrong? Can you phone your midwife and explain your worries?

I'm also not sure it can move, it moves in that as your uterus grows the position it is changes, but it is relative. It is very firmly implanted into the wall of your womb, surely you would have had a full abruption and the baby would have died if it had moved?