chocbunnies - DD was a big baby (over 4 kgs). Lessons I learned from that pregnancy & birth:
When doctor/midwife says "No problem, you can birth this baby", they mean "We will cut you up so he can come out".
If you will have so many stitches and such a big cut, please trust me, you'd rather have it on your belly where it's easy to keep clean & dry and not in your delicate bits that are so close to all the dirty 'plumbing'.
Seriously, if you are offered a c-section, take it. You don't get a medal for having birthed a big baby and your body takes a very long time putting the pieces back together. I only (!) had the huge episiotomy to deal with. One friend had a big baby and now has incontinence problems. Another has prolapse. C-section is 'major surgery' and all that but everyone I know who has had one has snapped back into their previous selves within weeks. If your next scan shows a big baby, do consider a c-section.
In the meanwhile, go easy on sugars (incl. fruits, cakes, chocolate) and slow sugars (carbohydrates - pasta, rice, bread, etc) if you want to increase your chances of a less chubby baby.
I'm in the same boat, by the way. I've been very careful with what I eat this pregnancy and put on only 8 kgs in 7 months. Yet we saw last scan that this baby is a little bit bigger than DD was at this stage. We will see how big he gets. If he is significantly over 4 kgs, doctor has agreed that I have suffered enough and will give me a c-section.