Your best bet is to ask your wife's OB/GYN about a prenatal supplement that also includes omega 3 supplementation. That way you are ensured that it is safe during pregnancy.
I see a nutritionist who prescribed Krill Oil for me to take during the pregnancy. He said it would be very good for the brain development of the baby. Everything I have read about it sounds positive, I would just like to have a second opinion if you don't mind.