J.H.
I am going through the exact same thing (I have a post on here somewhere about having a baby after 35). My husband is not completely sure yet if he wants a 3rd, so we haven't done anything yet...but I think a 3rd would be nice. However, it DOES change the dynamic. I was one of 3, and I babysit for a family of 3, and it seems that there is often the opportunity for "ganging up"--2 against 1--when kids play. As far as worrying about having a baby with "issues", the rate goes up with maternal age, but all in all, it is a gamble, really. You can control how you take care of your body, of course--take your prenatal vitamins, don't eat undercooked meat, stay away from fish--you know the drill! Other than that, I think it is all up to chance. You have to decide if you would be willing to take that chance...I say go for it! I am hoping we will too. :) Good luck with your decision!