My DH is not a crazy partier (especially since the pregnancy!), but does tend to go out on a Friday night for a fair few drinks with the guys, and now has a stag night coming up when I'll be 37+2...
I don't mind him going out, and know that the chances of very early delivery are pretty small, but at over 36 weeks and with the baby's head fully engaged, I'm nervous about having him not able to drive and frankly don't want anyone in the delivery room who's had anything to drink. He's said that he'll be 'careful', but after all the guys get together (and as most of our friends don't have any kids) this doesn't necessarily mean what I would think it means 
Did you have rules for your SO about this? What would you say is reasonable?