I think some women just have big babies and it's not always relevant to their adult size/weight.
I was 4lb 4oz at birth, average as an adult. My Mum had all smallish babies. My exH was also 4lb 4oz at birth and although 6ft, very slim build, around 9 1/2st. Yet DS1 was 9lb at term, DS2 10lb at 38 weeks and DS3 just under 7lb at 37 weeks, so none of them tiny. No GD as they tested me when they realised how big DS2 was.
I am now remarried and my DH is 6ft, average build and he was also a tiny baby. DD was estimated to be around 5lb 10oz at my 33 week scan this week, which is on the large side. I do have GD this time, but as baby ismeasuring big all over and my other DC were large babies, it seems she is simply big because of genetics and not the GD. They do tend to look for AC larger than other measurements when looking for indicators of GD.
Incidentally, all of my DS's are right skinny minnies now and average height, so haven't grown into big children, (in fact, DS1 is 50th centile height and 17th centile weight) I just seem to have big babies.