Isoimmunization and multifetal gestation Flashcards
definition: isoimmunization
immune response generated in an individual of one species by an alloantigen from a different individual of the same species
what is Rh disease?
occurs during pregnancy when there is n nincompatibility between the blood types of the mother and fetus
what is the inheritance pattern of Rh factor?
autosomal dominant
where is the maternal immune response to Rh generated?
spleen
what is the reason for neonatal jaundice as a result of Rh incompatibility?
fetus does not have glucoronyl transferase to conjugate indirect bilrubin
when is screening done for Rh status?
- first prenatal visit
- 28 weeks
- postpartum
- antepartum bleeding and before giving any Ig
what are the gold standard tests for Rh status?
- indirect Coombs
- direct Coombs
what is the indirect Coombs test?
- mix Rh(D)+ cells with maternal serum
- anti-Rh(D) ab will adhere
- RBCs then washed ans suspended in Coombs serum (antihuman Ig)
- RBCs coated with ab will be agglutinated
what is the direct Coombs test?
- mix infants RBCs with Coombs serum
- maternal ab present if cells agglutinate
what is the +Rh(D) antibody screen?
- serial ab titres q2-4 weeks
- if titre over 1:16 - get amniocentesis or MCA dopplers
- critical titre: significant risk of hydrops
what is the critical titre?
serial antidoby titres for Rh indicating significant risk for hydrops
what test is performed if there is a previously affected infant or critical titres are known?
amniocentesis
what is the significance of the zones on the Liley curve?
zone 1 - fetus very low risk of severe fetal anemia
zone 2 - mild to moderate risk of fetal hemolysis
zone 3 - severe fetal anemia with high probability of fetal death within 7-10 days
when is the Liley curve considered accurate?
after 27 weeks
how does the anemic fetus preserve oxygen delivery to the brain?
increasing flow
how is fetal anemia diagnosed?
- amniocentesis
- cordocentesis
- US
what are the treatment options for a fetus at risk of fetal anemia?
- intravascular fetal transfusion
- preterm birth
what are the results of Rh incompatibility?
- intrauterine fetal demise
- live born neonate appears pale, edematous, limp
- hyperbilirubinemia can lead to jaundice and neurotoxic effects
what are the treatment options for a fetus at risk of Rh incompatibility?
- phototherapy
- exchange or direct blood transfusion
what is RhoGAM?
anti-D Ig
what is the kleihauer-betke test? how does it work?
- % of fetal RBC in maternal circulation
- fetal RBCs contain HbF which is more resistant to acid elution than HbA so after exposure to acid, only fetal cells remain and can be identified with stain
how do dizygotic twins (fraternal) occur?
two separate ova fertilized by two separate sperm
how do monozygotic twins (identical) occur?
division of a fertilized ovum AFTER conception (1 in 250)
how do diamniotic / dichorionic twins occur?
division of the conceptus within 3 days of fertilization
how do diamniotic / monochorionic twins occur?
- division occurs between 4-8 days
- chorion has already begun to develop but amnion has not
how do monoamniotic / monochorionic twins occur?
- division occurs between 9-12 days after development of both amnion and chorion so they share a common sac
- occurs in 1 in 10,000
how do conjoined twins occur?
- division occurs incompletely
- 1 in 70,000
how is diagnosis made for multifetal gestation?
- size > dates on exam
- US at 9-10 weeks
when is chorionicity determined? what test?
9-10 weeks by US
what are the main risk / complication with multiple gestation?
preterm labor and delivery
twin-twin transfusion syndrome occurs in what type of multifetal gestation?
monochorionic > dichorionic
what are the morbidities / mortalities associated with monochorionic and dichorionic gestations?
- twin-twin transfusion syndrome
- cord entaglement
- fetal death
which carries more risk of morbidity / mortality: monochorionic or dichorionic gestation?
monochorionic
what is the etiology of twin-twin transfusion syndrome?
arterio-venous anastamosis between fetuses
what happens to the donor twin in twin-twin transfusion syndrome? recipient twin?
- donor twin: imparied growth, anemia, hypovolemia, oligohydramnios
- recipient twin: hypervolemia, HTN, polycythemia, high output CHF, polyhydramnios
