rhesus isoimmunization Flashcards
What is the prevalence of Rhesus D negativity among Caucasians?
15%
What are the three key steps in the occurrence of HDFN due to Rhesus isoimmunization?
- Rh-negative mother carries an Rh-positive fetus.
- Fetal cells enter maternal circulation, causing maternal sensitization.
- In a subsequent pregnancy, maternal antibodies cross the placenta and destroy fetal red cells.
Why does hemolysis not start during the first pregnancy?
IgM is produced in the first trimester and cannot cross the placenta. IgG is produced in subsequent pregnancies, leading to fetal hemolysis if sufficient.
What are the potential sensitizing events for Rhesus disease?
Abortion (spontaneous or induced)
Antepartum hemorrhage
Chorionic villus sampling
Amniocentesis
Cordocentesis
Multiple gestation
Delivery
Abdominal trauma
External cephalic version
Caesarean section
Manual removal of placenta.
What are the effects of Rhesus isoimmunization on the fetus during pregnancy?
Fetal anemia, Hydrops fetalis, Intrauterine fetal death.
What are the effects of Rhesus isoimmunization on the fetus following delivery?
Neonatal jaundice, Neonatal anemia, Early neonatal death, Brain damage from kernicterus, Delayed or abnormal developmental milestones.
How can Rhesus isoimmunization be prevented?
Anti-D prophylaxis within 72 hours of any sensitizing event, given at 28 and 34 weeks prophylactically.
What is the Kleihauer-Betke test?
A lab test used to detect and quantify fetal red blood cells in the maternal bloodstream to assess fetomaternal hemorrhage (FMH).
What are the clinical features of Hemolytic Disease of the Fetus and Newborn (HDFN)?
Fetal anemia, Hydrops fetalis, Kernicterus, Miscarriage, Early neonatal jaundice, Intrauterine fetal death.
What is Hydrops Fetalis?
Extracellular fluid in at least two compartments on ultrasound, some of this compartments include: skin edema (>5mm), pericardial effusion, pleural effusion, ascites.
How are unsensitized patients managed?
Rh antibody checked at booking, 28, 32, and 36 weeks.
≥250 IU of anti-D Ig within 72 hrs of a sensitizing event (12-20 weeks) or ≥500 IU of anti-D Ig if after 20 weeks.
500 IU (100 ug) RhoGAM given at 28 and 34 weeks.
500 IU (100 mg) RhoGAM within 72 hrs of delivery of an Rh-positive infant.
How are sensitized patients managed?
Monitor antibody levels every 2-4 weeks from booking.
What are the risk levels based on Anti-D levels?
Anti-D < 4 IU/mL: HDFN unlikely,
Anti-D 4-15 IU/mL: Moderate risk of HDFN,
Anti-D > 15 IU/mL: High risk of hydrops fetalis.
How is fetal anemia investigated?
Bilirubin concentration in amniotic fluid, Middle cerebral artery Doppler peak velocity measurement.
What is the role of amniocentesis in Rhesus isoimmunization?
Used to measure bilirubin concentration in amniotic fluid as an indirect measure of fetal hemolysis. First amniocentesis should be 10 weeks before the previous IUFD but not before 20 weeks.
What is the role of middle cerebral artery (MCA) Doppler in Rhesus isoimmunization?
Correlates well with fetal anemia. A raised MCA Doppler suggests a high probability of fetal anemia.
When should delivery occur in cases of Rhesus isoimmunization?
Delivery should take place in a unit with neonatal support, ideally at 36-37 weeks unless there are specific concerns such as fetal transfusion difficulty.
What investigations should be performed at delivery?
Cord blood should be taken for blood count, blood group, bilirubin level, and indirect antiglobulin test.
What is fetal blood transfusion and when is it needed?
A life-saving procedure for severely anemic fetuses that are too premature for delivery.
What are the characteristics of transfused blood for fetal blood transfusion?
Rhesus-negative, Cross-matched with maternal blood, Gamma-irradiated (to prevent GVHD), Packed (small volume used), Screened for infections (HIV, HBAg, CMV, etc.).
What are the routes for in-utero fetal blood transfusion?
Intra-umbilical, Intrahepatic, Intraperitoneal, Intracardiac.
