Rh Incompatibility and Disease

Август 5, 2022

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Rh Incompatibility and Disease

Содержание

2. Rh Disease Occurs during pregnancy when there is an incompatibility between the blood types of the
3. Blood Types A, B, O blood groups are specific types of proteins found on the surface
4. Rh Factor Proteins (antigens) occurring only on surface of RBC’s Rh + if proteins present Rh
5. Nomenclature Correct to say Rh(D) + or – Rh blood system has other antigens: C, c,
6. Why Does Rh Status Matter?
13. Pathophysiology Rh(D) antigen expressed by 30 d GA Many cells pass between maternal & fetal circulation
14. Pathophysiology cont… Initial IgM followed by IgG in 2 wks- 6 mths Memory B lymphocytes activate
17. Causes of RBC Transfer abortion/ectopic partial molar pregnancy blighted ovum antepartum bleeding special procedures (amniocentesis, cordocentesis,
18. General Screening ABO & Rh Ab @ 1st prenatal visit @ 28 weeks Postpartum Antepartum bleeding
19. Gold Standard Test Indirect Coombs: -mix Rh(D)+ cells with maternal serum -anti-Rh(D) Ab will adhere -RBC’s
20. + Rh(D) Antibody Screen Serial antibody titres q2-4 weeks If titre ≥1:16 - amniocentesis or MCA
21. U/S Parameters Non Reliable Parameters: Placental thickness Umbilical vein diameter Hepatic size Splenic size Polyhydramnios Visualization
23. Amniocentesis Critical titre/previous affected infant Avoid transplacental needle passage Bilirubin correlates with fetal hemolysis ∆ optical
25. Liley Curve Zone I – fetus very low risk of severe fetal anemia Zone II –
26. Middle Cerebral Artery Dopplers Measures peak velocity of blood flow Anemic fetus preserves O2 delivery to
27. Fetus at Risk Fetal anemia diagnosed by: amniocentesis cordocentesis ultrasound hydrops middle cerebral artery Doppler Treatment:
28. Infant at Risk Diagnosis: history of HDN antibodies? early jaundice cord DAT (“Coomb’s”) positive (due to
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Rh Disease
Occurs during pregnancy when there is an incompatibility between the

blood types of the mother and fetus

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Blood Types
A, B, O blood groups are specific types of proteins

found on the surface of RBC’s
Also found in the cells and other body fluids (saliva, semen, etc)
O represents neither protein being present on RBC
Possible groups include: A, B, AB, or O
A, B, O groups most important for transfusions

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Rh Factor
Proteins (antigens) occurring only on surface of RBC’s
Rh + if

proteins present
Rh – if proteins absent
A+, A-, B+, B-, AB+, AB-, O+, O-
Most important for pregnancy
Inheritance is Autosomal Dominant
15% Caucasian population is Rh-

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Nomenclature
Correct to say Rh(D) + or –
Rh blood system has other

antigens: C, c, D, E, e
D is by far the most common and the only preventable one
Weak D (Du) also exists
Also non Rhesus groups such as Kell, MNS, Duffy (Fy) and Kidd (Jk) exist

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Why Does Rh Status Matter?

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Pathophysiology
Rh(D) antigen expressed by 30 d GA
Many cells pass between maternal

& fetal circulation including at least 0.1 ml blood in most deliveries but generally not sufficient to activate immune response
Rh antigen causes > response than most
B lymphocyte clones recognizing foreign RBC antigen are formed

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Pathophysiology cont…
Initial IgM followed by IgG in 2 wks- 6 mths
Memory

B lymphocytes activate immune response in subsequent pregnancy
IgG Ab cross placenta and attach to fetal RBC’s
Cells then sequestered by macrophages in fetal spleen where they get hemolyzed
Fetal anemia

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Causes of RBC Transfer
abortion/ectopic
partial molar pregnancy
blighted ovum
antepartum bleeding
special procedures

(amniocentesis, cordocentesis, CVS)
external version
platelet transfusion
abdominal trauma
inadvertent transfusion Rh+ blood
postpartum (Rh+baby)

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General Screening
ABO & Rh Ab @ 1st prenatal visit
@ 28 weeks
Postpartum
Antepartum

bleeding and before giving any immune globulin
Neonatal bloods ABO, Rh, DAT

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Gold Standard Test
Indirect Coombs:
-mix Rh(D)+ cells with maternal serum
-anti-Rh(D) Ab will

adhere
-RBC’s then washed & suspended in Coombs serum (antihuman globulin)
-RBC’s coated with Ab will be agglutinated
Direct Coombs:
-mix infant’s RBC’s with Coombs serum
-maternal Ab present if cells agglutinate

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+ Rh(D) Antibody Screen
Serial antibody titres q2-4 weeks
If titre ≥1:16

- amniocentesis or MCA dopplers and more frequent titres (q1-2 wk)
Critical titre – sig risk hydrops
** amnio can be devastating in this setting
U/S for dating and monitoring
Correct dates needed for determining appropriate bili levels (delta OD450)

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U/S Parameters
Non Reliable Parameters:
Placental thickness
Umbilical vein diameter
Hepatic size

Splenic size
Polyhydramnios
Visualization of walls of fetal bowel from small amounts intraabdominal fluid may be 1st sign of impending hydrops
U/S reliable for hydrops (ascites, pleural effusions, skin edema) – Hgb < 70

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Amniocentesis
Critical titre/previous affected infant
Avoid transplacental needle passage
Bilirubin correlates with fetal hemolysis
∆

optical density of amniotic fluid @ 450nm on spectral absorption curve
Data plotted on Liley curve

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Liley Curve
Zone I – fetus very low risk of severe fetal

anemia
Zone II – mild to moderate fetal hemolysis
Zone III – severe fetal anemia with high probability of fetal death 7-10 days
Liley good after 27 weeks
98% sensitive for detecting anemia in upper zone 2/ zone 3

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Middle Cerebral Artery Dopplers
Measures peak velocity of blood flow
Anemic fetus preserves

O2 delivery to brain by increasing flow
Sensitivity of detecting severe anemia when MCA >1.5 MoM approaches 100%
Not reliable > 35 weeks GA

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Fetus at Risk
Fetal anemia diagnosed by:
amniocentesis
cordocentesis
ultrasound
hydrops

middle cerebral artery Doppler
Treatment:
intravascular fetal transfusion
preterm birth

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Infant at Risk
Diagnosis:
history of HDN antibodies?
early jaundice < 24

hours
cord DAT (“Coomb’s”) positive (due to HDN or ABO antibodies)
Treatment:
Phototherapy
Exchange or Direct blood transfusion

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Rh Incompatibility and Disease

Содержание

Rh DiseaseOccurs during pregnancy when there is an incompatibility between the

Blood TypesA, B, O blood groups are specific types of proteins

Rh FactorProteins (antigens) occurring only on surface of RBC’sRh + if

NomenclatureCorrect to say Rh(D) + or –Rh blood system has other

Why Does Rh Status Matter?

PathophysiologyRh(D) antigen expressed by 30 d GAMany cells pass between maternal

Pathophysiology cont…Initial IgM followed by IgG in 2 wks- 6 mthsMemory

Causes of RBC Transferabortion/ectopicpartial molar pregnancy blighted ovumantepartum bleeding special procedures

General ScreeningABO & Rh Ab @ 1st prenatal visit@ 28 weeksPostpartumAntepartum

Gold Standard TestIndirect Coombs:-mix Rh(D)+ cells with maternal serum-anti-Rh(D) Ab will

+ Rh(D) Antibody ScreenSerial antibody titres q2-4 weeks If titre ≥1:16

U/S ParametersNon Reliable Parameters: Placental thickness Umbilical vein diameter Hepatic size

AmniocentesisCritical titre/previous affected infantAvoid transplacental needle passageBilirubin correlates with fetal hemolysis∆

Liley CurveZone I – fetus very low risk of severe fetal

Middle Cerebral Artery DopplersMeasures peak velocity of blood flowAnemic fetus preserves

Fetus at RiskFetal anemia diagnosed by: amniocentesis cordocentesis ultrasound hydrops

Infant at RiskDiagnosis: history of HDN antibodies? early jaundice < 24

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