Hematology & oncology Clinical Case / MCQS / Uworld for Usmle step 2 / case 1

 Hematology & oncology Clinical Case  / MCQS / Uworld for Usmle step 2 / case 1 with answer and explanation and references and Educational objective

A healthy, 32-year-old, primigravid woman at 12 weeks of gestation comes to the physician for a routine prenatal visit. She has no complaints. She does not use tobacco or alcohol. She has blood group 0 , Rh(D)+, and her husband has blood group AB,

Rh(D)+. She is concerned about the risk of alloimmunization because her mother had that problem during her second pregnancy. Although the child will have a different blood group from the patient, alloimmunization is of little concern due to which of the following?

 

A.  Immune response is depressed in pregnancy . B.  ABO antigens are weakly antigenic . C.  The mother is tolerant to the child's ABO antigens . D.  Antibodies to ABO antigens cause mild disease in most newborns . E.  Antibodies to ABO antigens are not hemolytic .

 

Answer : D

Explanation:

The four common blood types are O, A, B, and AB. Patients missing a blood type have antibodies to the missing antigens as shown below.

 

Blood Type	Antibodies Against
A	B
B	A
O	Both A and B
AB	None

 

A mother with blood group 0 and a father with blood group AB will have a child with either blood group A or blood group B (both differ from the mother's blood group).

Hemolytic disease of the newborn (HDN) is mainly seen in a group 0 mother who has a group A or B baby. The A and B antigens are antigenic and cause the mother to form lgG antibodies to A or B that can cross the placenta (can also form some lgM antibodies to the A antigen and other minor antigens) (Choices A, B, and C). Only the lgG antibodies can cross the placenta, but varying titer levels result in HDN, which is mild in most patients, with neonatal jaundice successfully treated with phototherapy (Choice E).

However, the titers can be higher in certain populations (e.g., Africans and African Americans) and lead to more severe HDN.

 

ABO incompatibility reactions can occur in the first pregnancy because both A and B antigens are found in food and bacteria in the environment. These antigens can induce various degrees of antibody production in group O individuals. In contrast, Rh(D) alloimmunization reactions typically occur in the second pregnancy onwards, with greater severity. Also, Rh(D) antibodies are typically all lgG at higher titers that cross the placenta and cause more significant disease.

 

Exposure during the first pregnancy is usually required before causing disease in the second pregnancy. This patient has low risk of alloimmunization because both she and her husband are Rh(D)+.

 

Educational objective:

 

ABO incompatibility generally occurs in a group 0 mother with a group A or B baby, but ABO incompatibility causes less severe hemolytic disease of the newborn than does Rh(D) incompatibility. Affected infants are usually asymptomatic at birth with absent or mild anemia and develop neonatal jaundice, which is usually successfully treated with phototherapy.

 

References: 1.   The spectrum of ABO hemolytic disease of the newborn infant 2.   Maternal lgG anti-A and anti-B titres predict outcome in ABO-incompatibility in the neonate New links : 1.   The spectrum of ABO hemolytic disease of the newborn infant 2.   Maternal lgG anti-A and anti-B titres predict outcome in ABO-incompatibility in the neonate

 

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