Sorry Dee. I'm 5'4" and weighed 70kg before falling pg last time (this time I was 75) and was 94kg at the time I gave birth. No one ever mentioned increased risk to me?
Why do they weigh you anyway? I didn't think most places did that anymore?
In any case, if you are worried I'd suggest NOT dieting, or trying to lose weight, just keeping active. (I'm really trying to follow my own advice this time too!) If you do some LIGHT excersise, like frequent walks, and minimise really unhealthy stuff in your diet (course you can't go without too much of the yum stuff ) then you shouldn't put on too much weight. Plus, if you're active during pg it will help you to be more active during the birth. (I wish I had've been more active last pg!)
Finally, don't stress, babe. That wont help either you or your baby. And you are supposed to put on weight during pregnancy - it is totally normal. Where do they get that 6kg figure from?!? What if you have a 4kg baby?!?