(Science: haematology) A blood incompatibility between the mother and her baby. During childbirth if the mother is rh negative and the baby is Rh positive, blood can enter the maternal circulation (from the baby) sensitising the mother against rh factor. The mother's immune system will produce antibodies to Rh factor. In subsequent pregnancies, these maternal Rh antibodies can mix into the foetal circulation during childbirth. This will cause the rupture (haemolytic anaemia) of the baby's red blood cells.
See: newborn jaundice.