Most people (about 85%) are Rh-positive.
Rhesus incompatibility problems can occur in rhesus negative mothers, carrying rhesus positive babies. The problem doesn’t occur with first pregnancies because the antibodies aren’t present in the mother’s blood. However, in subsequent pregnancies, if the babies are rhesus positive, there may be a problem. The mother’s antibodies will cross over the placenta into the baby’s blood and, regarding it as ‘foreign’, will try to break it down.
Mismatched blood transfusions and previous miscarriage or trauma in the pregnancy are other risks for building up antibodies.
Rhesus status (i.e. negative or positive) does not affect fertility. A woman should be able to conceive (get pregnant) regardless of her blood group.
What rhesus affects is the survival of the fetus. If there is rhesus incompatibility, the baby may have problems while in the womb. If this is severe, the baby may not survive.