I don't know if it's 100% true but I read that if you go much over 10 days past the chances of Stillborn go up because the placenta doesn't work as well.
My 1st pregnancy I went 40+11days over. My doc induced me but I could not dilate so I had a c-section after 6hrs of trying. Everything did go smooth, no crazy complications, she weighed 10lbs 14oz lol so be prepared for a HEALTHY size baby.
Not me but a friend of mine had her third baby last summer at 43+2 (yes her dates were right on as they were trying and she was temping so knew exactly when she ovulated). She had a home birth, just like her first two babies, her midwife had been keeping an eye on her and knew baby and mom were both totally healthy and there was no need to induce. Baby was somewhere right around 8lbs and is now a beautiful healthy and perfect one-year-old girl.
After 42 weeks the placenta stops functioning as well and eventually starts to break down. It's dangerous to go passed 42 weeks.
Where I am they wont let you go more then 10days over so I don't know anyone who gone beyond that but I have had a friend who had the induction at 40+10 and everything went fine, just a big big baby.