I just discovered something neat at Babycenter. One thing I've really liked aobut the developmental weekly emails is the picture showing what the baby looks like inside the uterus that week. I just realized they also offer the picture for women having twins!
One thing I forgot to mention before was that the babies are at the point of viability. If for some reason they had to be delivered this week, they have a better than 50% survival rate. And that goes up every week we can keep them in there! So far, we've been really fortunate not to have any complications, and it'll hopefully stay that way.