If your child has a positive blood group, then there is the risk of your wife becoming "sensitised" if there is mixing of mother's and baby's blood in the pregnancy. If this happens, the first child will not have any problems, but future children will be at risk of severe anaemia, jaundice, swelling of the whole body and death, while in the womb.
This risk is very much avoidable if your wife has antiD injections once at twenty eight weeks of pregnancy , and again soon after delivery. She will need additional doses if she has any vaginal bleeds or hurts her abdomen during the pregnancy.
She will have to have the injections in every pregnancy, to prevent complications in the next one.