Hormones associated with pregnacy can range from having a extremely pouncy, horny wife to one that is just placid and un intersted in sex. and that can be the same extreme JUST for ONE woman :) Every woman is different and every pregnacy is different. You can try to encourage her and make sure she feels sexy, and you could be very successful at getting her in the mood every once in awhile.
So you can either wait it out, or try to gently convince her of her sexiness and try to seduce her in a nice romantic fashion.. your choice! :) just be nice to her. pregnant women can be very senstive to everything... :) And less stress she feels during, usually helps with delivery.. and that is not a fun expierience!