Rh disease, explained

Rh disease consists in a woman with Rh Negative blood has a child with Rh Positive blood. This can happen (about 75% of the time) 1 if the father is Rh Positive.  Throughout the pregnancy some of the fetus’ blood get into the mother’s bloodstream.  This is especially true during delivery.   The mother’s immune system detects an “invasion” and begins to make specific defenses (called antibodies) to destroy the “invaders” – the D antigens or Rh Factor proteins along with the red blood cells they are attached to.

Rh disease


Fortunately, it takes the immune system some time to develop these antigen-specific defenses, so the fetus during this first encounter is usually born unharmed.  But our immune system “remembers” threats – specific antigens – and how to fight them. This is why we do not generally get the same disease twice.  So now, our example Rh Negative mother is “sensitized” to the Rh Factor D antigen.  Should she get pregnant with another Rh positive fetus, her immune system will quickly send out Anti-D antibodies to attack if it detects the D antigen.  This is hemolytic disease of the fetus and new born (HDFN), and it poses a grave danger:  of miscarriage, stillbirth, early death or severe brain damage to the newborn.

Rh Negative blood is relatively uncommon – ranging from an incidence of 30% or more among the small population of Basques to a low of less than 1% among many Asian groups and around 15% among Europeans and North Americans of European descent.  But this still means that millions of pregnancies worldwide could be threatened by HDFN every year worldwide 2

1 Bowman JM. The prevention of Rh immunization. Transfus Med Rev.1988;2:129-150.
2 Bhutani VK, Zipursky A, Blencowe H, et al. Neonatal hyperbilirubinemia and rhesus disease of the newborn: incidence and impairment estimates for 2010 at regional and global levels. Pediatr Res 2013;74:86-100.

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