••• Chapter 20^ Rh Alloimmunization^207
❍ What are some common clinical factors associated with an increased risk of a substantial fetomaternal
hemorrhage?
Cesarean delivery, multiple gestation, manual removal of the placenta, placenta previa, placental abruption, and
intrauterine manipulation.
❍ How frequently is a fetomaternal hemorrhage noted in the first trimester?
Approximately 7%.
❍ How frequently is a fetomaternal hemorrhage noted in the second trimester?
16%.
❍ What percentage of Rh-negative mothers become sensitized prior to delivery without Rh immune globulin
prophylaxis?
1% to 2%.
❍ How early does the Rh antigen develop?
Rh antigens can be detected 38 days post conception.
❍ Can chorionic villus sampling performed on an Rh-negative patient result in sensitization?
Yes.
❍ What are two mechanisms thought to impact the risk of sensitization?
Approximately 10% to 20% of Rh-negative individuals are thought to be immunologic “nonresponders.” ABO
incompatibility exerts a protective effect against developing Rh sensitization.
❍ ABO incompatibility is associated with what risk of alloimmunization?
1% to 2% (without Rh immune globulin prophylaxis).
❍ What combination of ABO incompatibility is associated with the most protective effect?
Maternal blood type O, and fetal blood type A, B, AB.
❍ What is the definition of fetal hydrops?
Fetal hydrops is defined as the presence of excess fluid within at least two compartments of the fetal-placental unit.
❍ The fluid collections used in the definition of hydrops include?
Pericardial effusion, pleural effusion, abdominal ascites, scalp edema, polyhydramnios, or placentomegaly.
❍ What is the cause of fetal hydrops in the sensitized pregnancy?
Severe anemia (hemoglobin 7 g/dL or less) leads to fetal hydrops. This could be a result of tissue hypoxia secondary
to anemia causing increased capillary permeability.