Answer: The mother is Rh negative and the first child could be Rh negative and the second child Rh positive
Explanation:
Blood type occurs in two parts: the ABO system and another protein called the Rh factor.
When we inherit the ABO blood type from our parents the Rh factor is also inherited and can be either positive or negative.
When a mother,s blood is Rh negative and has a baby with a father that is Rh positive, then there's a possibility the children can either inherit the negative or positve Rh factor from either parent.
In this case, the mother pregnant has Rh negative blood type and her second (unborn) baby has a blood type of Rh positive.
Her immune system will detect this and perceive it as foreign invaders.
This will cause the mother's immune system to produce antibodies to attack the fetal blood, thus destroying the red blood cells of her unborn child and can result in HDN.
Since her first pregnancy was normal, her first child probably inherited Rh negative blood type.