Page 357 - Textbook of Pathology, 6th Edition

across the placenta into the circulation of the foetal red cells. placenta, while immune anti-A and anti-B antibodies which 341
Besides pregnancy, sensitisation of the mother may result are usually of IgG class may cross the placenta into foetal
from previous abortions and previous blood transfusion. circulation and damage the foetal red cells. ABO HDN occurs
HDN can occur from incompatibility of ABO or Rh blood most frequently in infants born to group O mothers who
group system. ABO incompatibility is much more common possess anti-A and/or anti-B IgG antibodies. ABO-HDN
but the HDN in such cases is usually mild, while Rh-D differs from Rh(D)-HDN, in that it occurs in first pregnancy,
incompatibility results in more severe form of the HDN. Coombs’ (antiglobulin) test is generally negative, and is less
severe than the latter.
PATHOGENESIS. The pathogenesis of the two main forms
of HDN is different. CLINICAL FEATURES. The HDN due to Rh-D incompa-
HDN due to Rh-D incompatibility. Rh incompatibility tibility in its severest form may result in intrauterine death
occurs when a Rh-negative mother is sensitised to Rh- from hydrops foetalis. Moderate disease produces a baby born
positive blood. This results most often from a Rh-positive with severe anaemia and jaundice due to unconjugated
foetus by passage of Rh-positive red cells across the placenta hyperbilirubinaemia. When the level of unconjugated
into the circulation of Rh-negative mother. Normally, during bilirubin exceeds 20 mg/dl, it may result in deposition of
pregnancy very few foetal red cells cross the placenta but bile pigment in the basal ganglia of the CNS called kernicterus
haemorrhage during parturition causes significant and result in permanent brain damage. Mild disease, however, CHAPTER 13
sensitisation of the mother. Sensitisation is more likely if the causes only severe anaemia with or without jaundice.
mother and foetus are ABO compatible rather than ABO
incompatible. Though approximately 95% cases of Rh-HDN LABORATORY FINDINGS. The haematologic findings
are due to anti-D, some cases are due to combination of anti- in cord blood and mother’s blood are as under:
D with other immune antibodies of the Rh system such as 1. Cord blood shows variable degree of anaemia, reticulo-
anti-C and anti-E, and rarely anti-c alone. cytosis, elevated serum bilirubin and a positive direct
It must be emphasised here that the risk of sensitisation Coombs’ test if the cord blood is Rh-D positive.
of a Rh-negative woman married to Rh-positive man is small 2. Mother’s blood is Rh-D negative with high plasma titre
in first pregnancy but increases during successive of anti-D.
pregnancies if prophylactic anti-D immunoglobulin is not
given within 72 hours after the first delivery. If both the COURSE AND PROGNOSIS. The course in HDN may
parents are Rh-D positive (homozygous), all the newborns range from death, to minimal haemolysis, to mental
will be Rh-D positive, while if the father is Rh-D positive retardation. The practice of administration of anti-Rh
(heterozygous), there is a 50% chance of producing a Rh-D immunoglobulin to the mother before or after delivery has
negative child. reduced the incidence of HDN as well as protects the mother
HDN due to ABO incompatibility. About 20% pregnancies before the baby’s RBCs sensitise the mother’s blood.
with ABO incompatibility between the mother and the foetus Exchange transfusion of the baby is done to remove the
develop the HDN. Naturally-occurring anti-A and anti-B antibodies, remove red cells susceptible to haemolysis and
antibodies’ which are usually of IgM class do not cross the also to lower the bilirubin level.

❑ Disorders of Platelets, Bleeding Disorders and Basic Transfusion Medicine