Alloimmunization/ Hydrops Flashcards
(37 cards)
The prevalence of red cell alloimmunization (in general) in pregnancy approximates
1%
Minimal amount that may cause sensitization
As little as 0.1 ml of fetal erythrocytes
Responsible genes for D antigen
2 genes
RHD And RHCE
Are located on the short arm of chromosome 1 and are inherited together.
The prevalence of D alloimmunization complicating pregnancy ranges from
0.5 to 0.9 percent.
Without anti-D prophylaxis, D-negative woman delivered of D-positive, ABO-compatible newborn has —% likelihood of developing alloimmunization.
16%
(2% at the time of delivery
7% by 6 min postpartum
And the remaining 7% will be stabilized) —producing detectable antibodies only in a subsequent pregnancy (Bowman, 1985).
Without anti-D prophylaxis, D-negative woman delivered of D-positive, ABO-INcompatible newborn has —% likelihood of developing alloimmunization.
2%
Sensitization to E, c and C antigens complicates approximately —% of pregnancies and accounts for about —% of red cell alloimmunization cases.
0.3%, 30%
(The most common is anti-E alloimmunization, but the need for fetal or neonatal transfusions is greater with anti-c alloimmunization than with anti-E or anti-C.
The most common cause of haemolytic disease of newborn
Incompatibility for the major blood group antigens A and B.
An estimated — to — % of foetuses from D-alloimmunized pregnancies will have mild to moderate haemolytic anaemia.
An estimated 25 to 30 % of foetuses from D-alloimmunized pregnancies will have mild to moderate haemolytic anaemia. And without treatment up to 25% will develop hydrous.
Intra-uterine Fetal transfusion complications
Fetal death (2 %)
Emergency caesarean (1%)
Infection and PPROM(0.3% for each)
Stillbirth (exceeds 15% if transfusion required before 20wks)
Overall survival rate of hydrops foetuses treated by Intra-Uterine Fetal blood transfusion
Approached 75-80 %
(Among 2/3 with resolution of hydrops following transfusion more than 95% survived, the survival rate was <40% if hydrops persisted.
What percent of alloimmunization occurs at the time of delivery?
90%
Routine postpartum administration of anti-D to at risk pregnancies within 72 hrs of delivery reduce the alloimmunization by
90%
Provision of anti-D Immunoglobulin at 28 wks reduce the 3rd trimester alloimmunization rate from approximately
2% to 0.1%
2 to 3 per 1000 pregnancies estimated their fetomaternal hge exceeds 30 ml of whole blood (15 of fetal RBCs) so single dose of Anti-D not sufficient, for this reason all D-negative women should be screened at delivery with
rosette test
( if positive to be followed by Quantitative test like kleihauer-Betke or flow cytometry tests
Me: All ? Is it Cost effective ?
The two responsible genes—RHD and RHCE —are located on the — arm of chromosome – and are inherited together, independent of other blood group genes.
The two responsible genes—RHD and RHCE —are located on the short arm of chromosome 1 and are inherited together, independent of other blood group genes.
D-negative individuals may become sensitized after a single exposure to as little as – mL of fetal erythrocytes (Bowman, 1988).
D-negative individuals may become sensitized after a single exposure to as little as 0.1 mL of fetal erythrocytes (Bowman, 1988).
the American College of Obstetricians and Gynecologists (2019a) has recommended that antibody titers not be used to monitor Kell-sensitized pregnancies. Why?
because Kell antibodies attach to erythrocyte precursors in the fetal bone marrow and thereby impair the normal hemopoietic response to anemia. With fewer erythrocytes produced, there is less hemolysis, and thus severe anemia may not be predicted by the maternal Kell antibody titer.
Incompatibility for the major blood group antigens A and B is the most common cause of hemolytic disease in newborns, but it does not cause appreciable hemolysis in the fetus. Why ?
This is because most anti-A and anti-B antibodies are IgM types and do not cross the placenta. Also, fetal red cells have fewer A and B antigenic sites than adult cells and are thus less immunogenic. Approximately 20 percent of newborns have ABO blood group incompatibility, although only 5 percent are affected clinically. In such cases, the resulting anemia is typically mild.
Of fetuses from D-alloimmunized pregnancies, – to – percent will have mild to moderate hemolytic anemia, and up to – percent have anemia severe enough to cause hydrops
Of fetuses from D-alloimmunized pregnancies, 25 to 30 percent will have mild to moderate hemolytic anemia, and up to 25 percent have anemia severe enough to cause hydrops
If alloimmunization is detected and the titer is below the critical value, the titer is generally repeated every – weeks for the duration of the pregnancy (American College of Obstetricians and Gynecologists, 2019a).
If alloimmunization is detected and the titer is below the critical value, the titer is generally repeated every 4 weeks for the duration of the pregnancy (American College of Obstetricians and Gynecologists, 2019a).
amnestic response ? Interesting
If a woman is sensitized from a prior pregnancy, her antibody titer may rise during the current pregnancy even if the current fetus is D-negative because of an amnestic response.
With immunoprophylaxis, however, the alloimmunization risk may be reduced to — percent. Despite long-standing and widespread use, its mechanism of action is not completely understood.
<0.2
Fetomaternal hemorrhage at delivery accounts for as many as – percent of alloimmunization cases. Routine postpartum administration of anti-D immune globulin to at-risk pregnancies within 72 hours of delivery lowers the alloimmunization rate by – percent (Bowman, 1985).
90 , 90
