Your story begins with understanding your blood type

What it means to be Rh-negative

The Rh Factor

The Rh factor is an antigen, or protein, that can be found on the surface of red blood cells. Rh is the abbreviation for rhesus, which is the name of one of many different blood group systems in the body.

Rh-positive People

+ Rh-positive people have the Rh antigen (also called D antigen) on the surface of their red blood cells

Rh-negative People

– Rh-negative people do not have the Rh antigen on the surface of their red blood cells

Rh-incompatibility: what does this mean?


The Rh factor is inherited from either the mother or the father. When an Rh-negative mother carries an Rh-positive baby, and some of the baby’s blood enters the mother’s bloodstream, this is called Rh-incompatibility. The mother’s immune system sees the baby’s red blood cells as “foreign” and will try to eliminate them as invaders by making anti-Rh antibodies. These antibodies can cross the placenta and attack the fetus’s red blood cells.

Rh-incompatibility usually does not affect the mother’s first baby, because her body does not have time to produce enough antibodies.

But once she has produced an immune response, or Rh sensitization, all future Rh-positive babies are at risk for developing hemolytic disease of the fetus and newborn (HDFN).

Approximately 15% of women are Rh-negative

Hemolytic disease of the fetus and newborn (HDFN)

Without prevention, HDFN is caused when the Rh-negative mother’s immune system tries to destroy her baby’s red blood cells. HDFN does not affect the mother, but it is a serious condition that affects the fetus and/or newborn and may cause:

  • Anemia
  • Jaundice
  • Heart failure
  • Possible brain damage
Cases of HDFN

When can Rh sensitization occur?

Rh sensitization can occur when a small amount of blood from the fetus mixes with the Rh-negative mother’s blood. This may happen during the following:

  • Delivery
  • Amniocentesis
  • Chorionic villus sampling (CVS)
  • Manipulative procedures (such as for a breech presentation)
  • Miscarriage
  • Ectopic pregnancy
  • Other obstetrical trauma

Preventing HDFN is better than needing to treat it, because serious problems can occur. When RhoGAM was first introduced in 1968, a single dose after delivery was found to lower the rate of Rh sensitization by 90%.1 But a small number of women were still becoming Rh sensitized for unknown reasons. Further studies found that Rh sensitization occurs at times other than just at delivery, but this can be reduced by 99% if Rh-negative mothers receive an anti-D therapy before delivery at 28 weeks.1,3,4

Since RhoGAM's introduction in 1968, the incidence of Rh sensitization has decreased dramatically.1,3,5

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