Given the autosomal recessive nature of the transmission of this disease, the probability of giving birth to a sickle cell child is 100% if both parents are sick with sickle cell disease, 50% if one of the parents is sickle cell while the other carries the sickle cell trait, 25% if both parents carry the sickle cell trait, and is zero if one parent is healthy - even if the other parent is sickle cell.