Yes there are health risks with having a baby while on those medications. You will want to practice birth control until you both decide to have a baby. At that time you will have to coordinate the pregnagcy with the OB GYN doctor and psychiatrist.
I know for sure than lithium can cause birth defects in the baby. It is the most harmful in the first trimester, and I think there are still risks of being on it after that. Lithium is known to cause heart defects, and other abnormalities. I am not sure if seroquel is safe or not, but I think it hasn't been on the market long enough for them to be sure.
Lamictal is a safer mood stabilzer to be one while pregnant. My sister-in-law has bipolar disorder and just had a baby. She was on lamictal during the pregnancy and as far as we can tell there was no complications. So, your wife just may have to switch meds. Again, you should discuss this issue with the psychaitrist. Women with bipolar disorder have had healthy babies before. So, your wife won't be the first to go through this.