Rh Disease

 

l Occurs during pregnancy when there is an incompatibility between the blood types of the mother and fetus



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


Rh Factor
l Proteins (antigens) occurring only on surface of RBC’s
l Rh + if proteins present
l Rh – if proteins absent
l A+, A-, B+, B-, AB+, AB-, O+, O-
l Most important for pregnancy
l Inheritance is Autosomal Dominant
l 15% Caucasian population is Rh-

Nomenclature
l Correct to say Rh(D) + or –
l Rh blood system has other antigens: C, c, D, E, e
l D is by far the most common and the only preventable one
l Weak D (Du) also exists
l Also non Rhesus groups such as Kell, MNS, Duffy (Fy) and Kidd (Jk) exist


Why Does Rh Status Matters

Pathophysiology
l Rh(D) antigen expressed by 30 d GA
l 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
l Rh antigen causes > response than most
l B lymphocyte clones recognizing foreign RBC antigen are formed
Pathophysiology cont…
l Initial IgM followed by IgG in 2 wks- 6 mths
l Memory B lymphocytes activate immune response in subsequent pregnancy
l IgG Ab cross placenta and attach to fetal RBC’s
l Cells then sequestered by macrophages in fetal spleen where they get hemolyzed
l Fetal anemia




Causes of RBC Transfer
l abortion/ectopic
l partial molar pregnancy
l blighted ovum
l antepartum bleeding
l special procedures (amniocentesis, cordocentesis, CVS)
l external version
l platelet transfusion
l abdominal trauma
l inadvertent transfusion Rh+ blood
l postpartum (Rh+baby)

General Screening
l ABO & Rh Ab @ 1st prenatal visit
l @ 28 weeks
l Postpartum
l Antepartum bleeding and before giving any immune globulin

l Neonatal bloods ABO, Rh, DAT

Gold Standard Test

l 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

l Direct Coombs:
-mix infant’s RBC’s with Coombs serum
-maternal Ab present if cells agglutinate

+ Rh(D) Antibody Screen
l Serial antibody titres q2-4 weeks
l If titre ≥1:16 - amniocentesis or MCA dopplers and more frequent titres (q1-2 wk)
l Critical titre – sig risk hydrops
l ** amnio can be devastating in this setting
l U/S for dating and monitoring
l Correct dates needed for determining appropriate bili levels (delta OD450)

U/S Parameters
l Non Reliable Parameters:
Placental thickness
Umbilical vein diameter
Hepatic size
Splenic size
Polyhydramnios
l Visualization of walls of fetal bowel from small amounts intraabdominal fluid may be 1st sign of impending hydrops
l U/S reliable for hydrops (ascites, pleural effusions, skin edema) – Hgb < 70 Amniocentesis l Critical titre/previous affected infant l Avoid transplacental needle passage l Bilirubin correlates with fetal hemolysis l ∆ optical density of amniotic fluid @ 450nm on spectral absorption curve l Data plotted on Liley curve Liley Curve l Zone I – fetus very low risk of severe fetal anemia l Zone II – mild to moderate fetal hemolysis l Zone III – severe fetal anemia with high probability of fetal death 7-10 days l Liley good after 27 weeks l 98% sensitive for detecting anemia in upper zone 2/ zone 3 Middle Cerebral Artery Dopplers l Measures peak velocity of blood flow l Anemic fetus preserves O2 delivery to brain by increasing flow l Sensitivity of detecting severe anemia when MCA >1.5 MoM approaches 100%
l Not reliable > 35 weeks GA.

Fetus at Risk
l Fetal anemia diagnosed by:
¡ amniocentesis
¡ cordocentesis
¡ ultrasound
hydrops
middle cerebral artery Doppler



l Treatment:
¡ intravascular fetal transfusion
¡ preterm birth


Infant at Risk
l Diagnosis:
¡ history of HDN antibodies?
¡ early jaundice < 24 hours ¡ cord DAT (“Coomb’s”) positive (due to HDN or ABO antibodies) l Treatment: ¡ Phototherapy ¡ Exchange or Direct blood transfusion Prevention l RhoGAM (120mcg or 300mcg) l Anti-D immune globulin l Previously 16% Rh(D)- women became alloimmunized after 2 pregnancies, 2% with routine PP dose, and 0.1% with added dose @ 28 wks Kleihauer-Betke Test l % fetal RBC in maternal circulation l Fetal erythrocytes contain Hbg F which is more resistant to acid elution than HbgA so after exposure to acid, only fetal cells remain & can be identified with stain l 1/1000 deliveries result in fetal hemorrhage > 30ml
l Risk factors only identify 50%

Kleihauer Calculations
l Fetal red cells = MBV X maternal Hct X % fetal cells in KB
newborn Hct

MBV – maternal blood volume (usually 5000ml)

Fetal cells X 2 = whole blood