MCQ Pathology Answer 11

The correct answer is B.

Women who are Rh negative are at risk for developing Rh isoimmunization. Rh isoimmunization occurs when an Rh-negative mother becomes exposed to the Rh antigen on the red blood cells of an Rh-positive fetus. This exposure may lead the mother's immune system to become sensitized to the Rh antigen such that in a future pregnancy with an Rh-positive fetus, the mother's immune system may "attack" the Rh antigen on the fetal red blood cells. This immune response may lead to the development of fetal anemia, hydrops, and death.

To prevent Rh isoimmunization from occurring, Rh-negative women who are not Rh alloimmunized should receive RhoGAM (anti-D immune globulin) at 28 weeks' gestation, within 72 hours after the birth of an Rh-positive infant, after a spontaneous abortion, or after invasive procedures such as amniocentesis. RhoGAM should also be strongly considered in cases of threatened abortion, antenatal bleeding, external cephalic version, or abdominal trauma.

The amount that is usually given after the delivery of an Rh-positive fetus is 300 µg. This amount is sufficient to cover a fetal to maternal hemorrhage of 30 mL (or 15 mL of fetal cells). However, some women will have a fetal to maternal hemorrhage that is in excess of this 30 mL-especially in cases such as manual removal of the placenta (like this patient had) or placental abruption.

To determine the amount of fetal to maternal hemorrhage that occurred, it is necessary to perform a Kleihauer-Betke test. This acid-dilution procedure allows fetal red blood cells to be identified and counted. Knowing the amount of fetal to maternal hemorrhage that took place allows the correct amount of RhoGAM to be given.

A complete blood count (choice A) will demonstrate the amount of maternal hemorrhage, but not the amount of fetal to maternal hemorrhage.

Liver function tests (choice C), prothrombin time (choice D), and serum potassium (choice E) do not allow for the determination of the amount of fetal to maternal hemorrhage.

Category: Pathology MCQs