Isoimmunizations and Multifetal gestations Flashcards
What is alloimmunization (isoimmunization)?
Immune response generated in an individual of one species, by an alloantigen from a different species
What is on the A antigen? B?
A = N-acetyl galactosamine B = Galactosamine
What does it mean to be Rh +?
Have the big D antigen
What is the inheritance pattern of Rh?
AD
What percent of the population is Rh negative?
15%
When is Rh status a concern?
If mother is Rh negative, and fetus is Rh positive
How does Fetal anemia 2/2 Rh status occur?
IgG antibodies cross placenta, attacking RBCs
Which antibodies can cross the placenta?
IgG
When in gestation do the Rh antigens get expressed by baby?
30 days
What is the significance of the 0.1 ml of blood the passes between mother and fetus during a normal delivery?
Not large enough to cause a response, but more than that and an immune response can take place
Where do the RBCs in the fetal circulation get broken down at? What happens?
Spleen
Jaundice, and kernicterus
What are the causes of RBC transfer?
-Abortion/ectopic
-Abdominal trauma
-
What are the procedures that can cause RBC transfer? (3)
Amniocentesis
Cordocentesis
Chorionic villus sampling
Can a partial molar pregnancy cause RBC transfer?
yes
When are mothers screened for RH incompatibility?
- At the 1st prenatal visit
- 28 weeks
- Postpartum
What is the indirect Coombs test?
Mix Rh+ cells with maternal serum,
anti-Rh Ab will adhere
What is the direct Coombs test?
Infants RBCs + coombs serum
How do you follow women who have antibodies to Rh +?
- Serial Abs q2-4 weeks
- If titre more than 1:16, then amniocentesis and increase 1-2 weeks
What happens when the critical value of the Ab titer (for Rh) is hit?
Significant risk for hydrops
When should amniocentesis never be performed on an Rh - woman?
When she has high levels of Ab against Rh +
Which of the following US parameters is useful for determining the risk for fetal anemia 2/2 Rh antigen:
- skin edema
- Placental thickness
- Umbilical vein diameter
- Hepatic size
- Pleural effusions
- Splenic size
- Polyhydramnios
- Ascites
- ascites
- pleural effusions
- Skin edema
True or false: the amount of bilirubin sampled in an amniocentesis correlates with the amount of fetal hemolysis
True
True or false: you should avoid transplacental needle passage with amniocentesis
True
What is the Liley curve, and what is it used for? When is this accurate?
Plots bili values and determines the risk to the fetus
Godd after 27 weeks
What is the risk level for zones I-III on the liley curve?
I = Very low risk II = Mild to moderate III = severe fetal anemia with high probability of death
Why is the middle cerebral artery flow dopplered instead of other arteries? When is this no longer reliable?
Blood flow is preserved to the brain
Not reliable after 35 weeks
What is the sensitivity of middle cerebral artery doppler in detecting severe anemia?
Near 100%
What are the two treatment options for fetal anemia?
- Intravascular fetal transfusion
- Preterm birth
How do you diagnose hemolytic disease of the newborn (HDN) after birth?
Watch for early jaundice
Cort DAT positive
What is the treatment for HDN?
- Bili lights
- Blood transfusion exchange
What is RhoGAM?
Anti-D immunoglobulin
What is the Kleihauer-Betke test? How does this work?
Test to assess the percent of RBC in maternal circulation
Difference in acid elution rates between HbF and HbA allows for separation
300 mcg of Rhogam covers how many ml of fetal cells? Fetal Whole blood?
15 mL or 30 mL of whole blood
What is the calculation to determine Fetal red cells?
MBV x Maternal HCT x%fetal cells in KB /newborn HCT
What is the incidence of multifetal gestation?
1 in 90
What causes dizygotic twins?
Two separate ova fertilized by two separate sperm
What causes monozygotic twins?
Division of a fertilized ovum after conception
In whom are dizygotic twins common? (2)
- Older mother
- Higher parity
What is a diamniotic/dichorionic pregnancy? When does it occur?
Division of the conceptus within 3 days of fertilization
What is a diamniotic/monochorionic pregnancy? When does it occur?
division occurs occurs between 4-8 days
What is a monoamniotic/monochorionic pregnancy? When does it occur?
Division occurs between 9-12 days after development of both amnion and chorion
What is the amnion?
The innermost membrane that encloses the embryo
What is the chorion?
the outermost membrane surrounding an embryo
What are the major issues with monoamniotic/monochorionic pregnancies?
Potential for cord ties and other issues
When should you suspect twin pregnancies?
Size greater than dates on exam
When can chorionicity be determined on US?
9-10 weeks
What are the risks with multiple gestations? (4)
- Anemia
- Operative delivery
- Discordant growth
- Hydramnios
What determines discordant growth in twins?
When one is 20% larger than the other
Why is there an increased risk for antepartum bleeding with twins?
Abnormal placentations
Why is there a risk of postpartum hemorrhage with twins?
Distended uterus muscle has problem contracting
What is twin-twin transfusion syndrome?
Monochorionic gestation, where AV anastomosis in the placental bed between the two fetal circulations, with one baby stealing blood from the other
What are the complications from twin-twin transfusion syndrome?
- Impaired growth/anemia/hypovolemia in one
- Hypervolemia, HTN, polycythemia in the other
In what type of pregnancies does twin-twin transfusion syndrome occur?
Monochorionic
If twins are going to be delivered vaginally, what does this depend on?
Upon the presenting twin presentation
Why is it better if the first twin delivered vaginally is biggest than the second?
Ensures that the second one will fit through, even if breech
What is a double set up?
Having both c-section tools and vaginal birth tools ready
How many teams are there for multiple fetuses?
As many kids as there are
