fetus attains the maternal level at about 33 weeks. At term (40 weeks), the mean IgG
level of cord blood may be 20 to 30 percent higher than that of maternal blood.
2-16. CLINICAL AND LABORATORY FEATURES OF HEMOLYTIC DISEASE
a. Pathophysiology of Hemolytic disease. When the fetal RBCs become
sensitized with maternal antibody, they are removed from the circulation by the
reticuloendothelial system. The biIirubin produced from the RBC destruction crosses
the placenta to the maternal circulation, where it is removed by the maternal liver. The
resulting anemia causes the hematopoietic tissue of the fetus to respond by
proliferating, and increasing the production of new RBCs, many of which are released
prematurely into the circulation, resulting in increased numbers of reticulocytes and
nucleated RBCs. The liver and spleen enlarge since much of the fetal hematopoietic
tissue is located in these organs. If the immune destruction is severe, the fetal
hematopoietic tissue cannot completely compensate for the loss of RBCs and the fetus
becomes increasingly anemic. Severe anemia may lead to heart failure with
generalized edema (hydrops fetalis), sometimes resulting in intrauterine or neonatal
death. If the baby is live-born and not hydropic, the principal danger lies in the
accumulation of unconjugated bilirubin. Destruction of the fetal red blood tells
continues, but the maternal mechanism for excreting bilirubin is no longer present. The
liver of the premature and newborn infant is unable to conjugate and excrete bilirubln
effectively because of a temporary deficiency of the enzyme glucuronyritransferase. If
the amount of unconjugated biIirubin exceeds the albumin-binding capacity, the
unbound, unconjugated biIirubin may then diffuse into the tissue cells and result in
kernicterus that is often fatal or responsible for permanent brain damage.
b. Laboratory Features of HEMOLYTIC DISEASE.
(1) The most useful initial index of the severity of the hemolytic process is
the cord hemoglobin; however, one cannot use it as a means of subsequently excluding
the need for exchange transfusion for hyperbilirubinemia. Three clinical groups may be
defined as follows:
Cord Hemoglobin in gm/dl *
*Normal cord hemoglobin is 13.6 to 19.6 gm/dl, although this may vary slightly among
(2) When blood is by heel prick, the hemoglobin values are often several
grams per deciliter higher than in cord blood.