I'm about the same size as you - apparently 'normal' pelvis - and had a 4.29kg baby at 42 weeks gestation. Due to fetal distress, the OB pulled him out with forceps. I figure if I'm flat on my back with legs in stirrups (ie, pelvis at smallest) and I can still fit forceps and a baby then I can birth a much bigger one in a better position.
I think the main determinant of a baby's size at birth is the functioning of your placenta. There's not much you can do about it unless you want to take up smoking...? That restricts blood flow to the placenta and can reduce baby's birth weight.