Cause of HDN
Newborn's RBCs are being attacked by antibodies from the mother. Attack beings in the womb and is caused by an incompatibility between the mother's and baby's blood.
Pregnancies at risk of HND
*are those in which an Rh D-negative mother becomes pregnant w/ a RhD-positive child
*(D antigen inherited from Dad)
*Mom's immune response is to form antibodies (anti-D) against it
anti-D
*usually of the IgG type
*(this is the type that is transported across the placenta and therefore delivered to the fetal circulation)
Other pregnancies at risk
*incompatibility of the ABO blood group
*arises when a mom w/ O blood becomes pregnant w/ a fetus of a different blood type (A, B, or AB)
*mom's serum has naturally occuring anti-A and anti-B (which of course tend to be class IgG)
When antigens cross the placenta, they...
hemolyse fetal RBCs
ABO incompatibility is usuaally ______ severe than Rh incompatibility
less
Sensitization occurs
During the pregnancy w/ a Rh+ baby or with a blood transfusion
*once a mom has been sensitized, her blood will contain antigen
*at time of sensitization, antigen is of IgM type and does not cross the placenta...repeat encounter (next pregnancy), antigen I
Direct Coombs test
*confirms the presence of anti-D (and that the mom has been sensitized)
In mild cases, newborn symptoms include
*mild anemia & jaundice
*both may resolve w/out tx
In more severe cases, newborns...
*may develop kernicterus, a potentially fatal condition that leaves permanent brain damage to babies that do survive
*due to bilirubin entering brain
Even more severe cases, newborns...
*severe anemia; liver, spleen, and other organs try to compensate and hepatosplenomegaly and liver dysfunction can occur. Plus a complication is hydrops fetalis
hydrops fetalis
Complication of severe HDN
Fetal tissues become swollen
Usually fatal either n utero or soon after birth
direct Coombs test
detects maternal anti-D antibodies that have already bound to fetal RBCs
Indirect Coombs test
finds anti-D antibodies in the mom's serum
*by finding maternal anti-D before fetal RBCs have been attacked, tx can be given to prevent or limit the severity of HDN
Prevention against Rh D sensitization
Usually Rh D-negative moms receive an injection of anti-D Ig at about 28 wks gestation, and another dose at about 34 wks gestation, and final dose given after baby has been delivered
Routine prophylaxis for HDN caused by incompatibility of other blood group antigens
None :(
Determine whether the fetus is at risk
If maternal anti-D has been confirmed, next step is to determine if fetal RBCs are targets:
*If dad is homozygous for D (D/D)...fetus will be D+
*if dad is heterozygous (D/d), baby has 50/50 chance...only way to tell is to test fetal cells from amniotic f
If fetus is Rh-D+
*Carefully monitor pregnancy for sings of HDN including ultraosounds of fetus and amount of anti-D in mom's serum
Fetal tx
if fetal anemia is confirmed, a blood transfusion may be done IN UTERO to replace the lysed fetal RBCs in severe cases
*transfusions may also be done in newborn period