If a fetus has an rh negative mother and an rh positive father, will a miscarriage occur?

Not if first preg.: Rh sensitization usually occurs after delivery of a child who is Rh +, and mom is -. Fetal blood may mix with maternal blood. If not given Rhogam (antibodies against Rh + blood) her immune system will be sensitized to Rh+. Fathers who are Rh+ may be carriers of Rh - , with 50% chance of an Rh - infant with no risk. Even if sensitized, fetal therapy can allow survival of an Rh + baby.