Be careful what you wish for! If she does hit the heavy 3rd trimester hornys you have to deal with the fact that she may be very demanding about her needs! And things "down there" can get a little thick and "cheesy" towards the end.....and you may have to be "down there" alot more than you are "in there"! But I'm sure you love your wife and will do what is needed. My most memorable sexual moments were fucking from behind and holding onto that big belly! The problem was at that point I was feeling this deep intimacy and she wanted to be fucked hard and often and when she was done she wanted me to GO AWAY.....then an hour later do it again!
The real fun comes in working out your sex life post-partum!