Well I went with 41 weeks, but to be specific 10 days past EDD is my max. I've read and been told by Dr's that after 10 days the % of intra-utero death increases so I would just be panicking after that.

Having said that, my babies came DD1 2 days early and DD2 right on her EDD, so I haven't had to face it, but I was prepared to go 10 days over with DD2 as I was hoping she'd get a bit fatter if I did, as long as I was monitored continuously. (Maybe I'm a bit more paranoid than some though, DD1 was IUGR and no-one even knew about it, so think fundal height measurements is a crock, and worrying my babies are starving inside me doesn't make one want to prolong their birth.)