Rh incompatibility occurs when the mother's blood type is Rh negative and her fetus' blood type is Rh positive.
If some of the fetus' blood passes into the mother's blood stream, her body will produce antibodies in response.
These antibodies could pass back through the placenta and harm the fetus' red blood cells, causing mild to serious anemia in the fetus.
A.D.A.M. Editorial Team: David Zieve, MD, MHA, and David R. Eltz. Previously reviewed by Kimberly G Lee, MD, MSc, IBCLC, Associate Professor of Pediatrics, Division of Neonatology, Medical University of South Carolina, Charleston, SC. Review provided by VeriMed Healthcare Network (2/10/2011).