15 - Fetal Disorders Flashcards
Results from transplacental passage of maternal antibodies that destroy fetal red cells
Red cell alloimmunization
What does alloimmunization lead to, defined as overproduction of immature fetal and neonatal red cells?
Erythroblastosis fetalis / hemolytic disease of the fetus and newborn
Other possible causes of fetal anemia
Viral (parvovirus B19), alpha4-thalassemia, fetomaternal hemorrahge
Methods through which fetal anemia may be identified
Fetal blood sampling, or Doppler evaluation of fetal middle cerebral peak systolic velocity
Consequences of progressive fetal anemia
Heart failure, hydrops fetalis, death
Prevalence of red cell alloimmunization in pregnancy
1%
Test used to determine unbound antibodies in maternal serum
Indirect Coomb’s
Clinically important group of antigens formerly termed Rh or rhesus groups
C, D, E groups
Minimum amount of fetal erythrocytes that may lead to maternal sensitization within Rh / CDE alloimmunization
0.1 ml
Prevalence of D alloimmunization complicating pregnancies
0.5 to 0.9%
Likelihood that Rh / D-negative woman delivered of D-positive, ABO-compatible newborn will develop alloimmunization (without prophylaxis)
16%
Distribution of sensitization of Rh / D-negative alloimmunization (at delivery, 6 months postpartum, subsequent pregnancy)
Delivery - 2%, 6-months postpartum - 7%, subsequent pregnancy - 7%
Likelihood that Rh / D-negative woman delivered of D-positive, ABO-INCOMPATIBLE will develop alloimmunization (without prophylaxis)
2%
Reason why Rh (+), ABO incompatible fetus produces less alloimmunization than an ABO compatible one
Erythryocyte destruction of ABO-incompatible cells, limiting sensitizing opportunities
Fetomaternal hemorrhage, pregnancy loss related causes of red cell alloimmunization
Ectopic pregnancy, spontaneous abortion, elective abortion, fetal death
Fetomaternal hemorrhage, procedure related causes of red cell alloimmunization
Chorionic villus sampling, amniocentesis, fetal blood sampling, evacuation of molar pregnancy
Fetomaternal hemorrhage, other related causes of red cell alloimmunization
Delivery, abdominal trauma, abruptio, unexplained vaginal bleeding during pregnancy, manual placental removal, external cephalic version
What is the grandmother effect of red cell alloimmunization
If maternal Rh + blood enters fetal circulation (Rh -), that fetus may subsequently develop antibodies during adulthood that will then cause alloimmunizatioin in an Rh + child (the grandchild of the original Rh + woman)
Minor antigens / minor blood groups that may result in red cell alloimmunization
Kell antigens (most common), Duffy group, Kidd group
T or F: While ABO incompatibility is the most common cause of hemolytic disease of the newborn, it does not cause appreciable hemolysis in the fetus
True
Reason why ABO incompatibility is more of a pediatric (neonate) and not obstetric disease (fetus)
Because the IgM antibodies do not cross the placenta
Percentage of fetuses from D-alloimmunized pregnancies that will have mild to moderate hemolytic anemia
25 to 30%
Percentage of those with D-alloimmunization that will develop hydrops fetalis if no treatment is given
25%
Frequency of titer monitoring if alloimmunization is detected but titer value is below the critical level
Every 4 weeks
T or F: Serial titer assessment is indicated if a prior pregnancy was complicated by alloimmunization
False - the subsequent pregnancy is assumed to be at risk regardless of titer level
Initial evaluation of alloimmunization begins with?
Determination of paternal erythrocyte antigen status
T or F: If the father is negative for the red cell antigen to which the mother is sensitized, the pregnancy is not at risk
True
The recommended test for detection of fetal anemia
Serial measurement of peak systolic velocity of fetal MCA
