208 Obstetrics and Gynecology Board Review •••
❍ What process can lead to nervous system damage?
Hyperbilirubinemia can lead to kernicterus. When levels of total serum bilirubin exceed 25 mg/dL, unconjugated
bilirubin can enter brain tissue and cause apoptosis and necrosis. This leads to acute bilirubin encephalopathy that
may result in permanent neurologic damage (kernicterus).
❍ 0.1% to 0.2% of susceptible Rh-negative women still become alloimmunized despite recommendations for
immunoprophylaxis. Why is this?
(1) Failure to administer anti-D immune globulin at 28 to 29 weeks’ gestation.
(2) Failure to recognize clinical events that place patients at risk of alloimmunization and administer anti-D
immune globulin, when indicated.
(3) Failure to administer in a timely fashion anti-D immune globulin postnatally, when indicated.
❍ What amount of fetomaternal hemorrhage is necessary to cause alloimmunization?
The exact amount varies. Alloimmunization may occur with exposure to as little as 0.1 mL of Rh-positive red cells.
❍ What is the associated risk of Rh alloimmunization in susceptible patients under the following
circumstances: spontaneous abortion... induced abortion?
Spontaneous first trimester abortion: 1.5% to 2%.
Induced abortion: 4% to 5%.
❍ What is the risk of fetomaternal hemorrhage under the following circumstances: chorionic villus
sampling... amniocentesis... external cephalic version?
Chorionic villus sampling: 14%.
Amniocentesis: 7% to 15%.
External cephalic version: 2% to 6%.
❍ What laboratory studies should every woman have at the first prenatal visit (with regard to
alloimmunization)?
ABO blood group.
Rh type.
Antibody screen.
❍ Who should be given Rh immune globulin during pregnancy?
Rh-negative mothers with a negative antibody screen and a father of the pregnancy who is Rh-Positive or who has
unknown status.
❍ When is Rh immune globulin given during an otherwise uncomplicated pregnancy?
28 weeks (and within 72 hours of delivery if fetus is Rh-positive).
❍ What is the standard dose of Rh immune globulin used in the United States?
300 mg.
❍ How does Rh immune globulin work?
Rh immune globulin works by binding RhD antigen on fetal cells in maternal circulation. Because the fetal RhD
antigens are “covered” by the Rh immune globulin, the mother does not develop her own antibodies to RhD.