I'm 31 weeks and still wearing mine. I think the cold weather helps. I can't wear my engagement ring when I'm NOT pregnant during the summer, because hot weather makes my fingers swell. I got my wedding ring in a slightly larger size than my engagement ring for this reason. I can at least wear one of my rings in the summer, and since my wedding ring is way too big in the winter, my engagement ring keeps it from falling off. ;-)
I suspect I may have to give up my engagement ring before this pregnancy is over, but I think I won't have a problem with the wedding ring.