My fundal height as of yesterday was 21 weeks and I am only 17+5. The number of pregnancies, position of baby, amniotic fluid volume, build of mama are all factors.
My babies have all been 9lb + except for DD3 who was 6lb ish. Her birth was no easier than my big babies. I didn't tear with my DD4 or DS6 either.
If you don't have an illness our bodies rarely grow babies too big for our bodies.

Wishing you lots of luck and good wishes for bringing your new baby into the world.