The “Rh Disease” Explained

Rh D Hemolytic disease of the newborn or Rh disease

Rh disease (also known as rhesus isoimmunization, Rh (D) disease) is a type of hemolytic disease of the fetus and newborn (HDFN). HDFN due to anti-D antibodies is the proper and currently used name for this disease as the Rh blood group system actually has more than 50 antigens and not only D-antigen. The term “Rh Disease” is not the current terminology but it is commonly used to refer to HDFN due to anti-D antibodies, and prior to the discovery of anti-Rh_o(D) immune globulin, it was the most common type of HDFN. The disease ranges from mild to severe, and occurs when Rh-D negative women with anti-D antibodies present are pregnant with an Rh-D positive fetus.

There are several reasons why an Rh-D negative woman might carry anti-D antibodies.

Among those:

1. She has previously carried (successfully or unsuccessfully) an Rh-D positive fetus.
2. She has had a blood transfusion containing Rh-D positive blood.
3. Her mother is Rh-D positive and while in her womb, her blood got in contact with hers.

Approximately 50% of Rh-D positive infants with circulating anti-D are either unaffected or only mildly affected requiring no treatment at all and only monitoring. An additional 20% are severely affected and require transfusions while still in the uterus. This pattern is similar to other types of HDFN due to other commonly encountered antibodies (anti-c, anti-K, and Fy(a)).

In an RhD negative mother, Rho(D) immune globulin can prevent temporary sensitization of the maternal immune system to RhD antigens, which can cause rhesus disease in the current or in subsequent pregnancies. With the widespread use of RhIG, Rh disease of the fetus and newborn has almost disappeared in the developed world. The risk that an RhD negative mother can be alloimmunized by a RhD positive fetus can be reduced from approximately 16% to less than 0.1% by the appropriate administration of RhIG.

Hemolytic disease of the newborn (HDN)

The hemolytic condition occurs when there is an incompatibility between the blood types of the mother and fetus. There is also potential incompatibility if the mother is Rh negative and the father is positive. When any incompatibility is detected, the mother often receives an injection at 28 weeks gestation and at birth to avoid the development of antibodies towards the fetus. These terms do not indicate which specific antigen-antibody incompatibility is implicated. The disorder in the fetus due to Rh D incompatibility is known as erythroblastosis fetalis.

• Hemolytic comes from two words: “hema” (blood) and “lysis” (solution) or breaking down of red blood cells
• Erythroblastosis refers to the making of immature red blood cells
• Fetalis refers to the fetus.

When the condition is caused by the Rh D antigen-antibody incompatibility, it is called Rh D Hemolytic disease of the newborn or Rh disease. Here, sensitization to Rh D antigens (usually by feto-maternal transfusion during pregnancy) may lead to the production of maternal IgG anti-D antibodies which can pass through the placenta. This is of particular importance to D negative females at or below childbearing age, because any subsequent pregnancy may be affected by the Rh D hemolytic disease of the newborn if the baby is D positive. The vast majority of Rh disease is preventable in modern antenatal care by injections of IgG anti-D antibodies (Rho(D) Immune Globulin). The incidence of Rh disease is mathematically related to the frequency of D negative individuals in a population, so Rh disease is rare in old-stock populations of Africa and the eastern half of Asia, and the Indigenous peoples of Oceania and the Americas, but more common in other genetic groups, most especially Western Europeans, but also other West Eurasians, and to a lesser degree, native Siberians, as well as those of mixed-race with a significant or dominant descent from those (e.g. the vast majority of Latin Americans and Central Asians).

• Symptoms and signs in the fetus:
  • Enlarged liver, spleen, or heart and fluid buildup in the fetus’ abdomen seen via ultrasound.
• Symptoms and signs in the newborn:
  • Anemia that creates the newborn’s pallor (pale appearance).
  • Jaundice or yellow discoloration of the newborn’s skin, sclera or mucous membrane. This may be evident right after birth or after 24–48 hours after birth. This is caused by bilirubin (one of the end products of red blood cell destruction).
  • Enlargement of the newborn’s liver and spleen.
  • The newborn may have severe edema of the entire body.
  • Dyspnea (difficulty breathing)

See also:

Rh Negative History