High AB ratio

Hello

I am just after some info on the AB ratio, i know it is to do with the blood flow thru the umbilical cord to baby. At my 32 week scan ( because of GD) the ratio was at the upper limits for how many weeks i was. It was 3.4. I seen my OB today and she said it was too high and i am having another scan tomorrow to see if it has gone up. I am 35 weeks now and i was wondering what this means if it is high, what do they do. And can it harm bubs? i see her Mon but am interested to know more about this. She seems a bit worried and in a hurry for the scan to be done.
I was already prepared for bubs to be a little bit early due to GD but not sure if they will bring me on earlier then that if this ratio is a problem???

Any info will be greatly appreciated.:(