Rhesus Isoimmunization – Screening, Monitoring & Management

Rhogam Dosing (Anti-D)

Prevention of Isoimmunization

• Estimation of maternal fetal blood can be done using the Kleihauer-Betke test.
• The standard dose of anti-D is 0.3 mgZ, which will eradicate 15 ml of fetal red blood cells (RBC) or 30 mls of fetal whole blood.Z
• Schedule for injection:

Trimester/Procedure	Dose
Antepartum bleeding 1st trimester	50 μg RhIgG
Antepartum bleeding 2nd & 3rd	300 μg RhIgG
Prophylaxis GA 28-32 weeks	300 μg RhIgG
Delivery	<72 hr - 300 μg RhIgG

7M & 78h from birth doses

Kleihauer-Betke Test

Detection of Fetomaternal Hemorrhage

• Used for detecting Fetomaternal or Transplacental Hemorrhage.

• The test is dependent on the fact that adult hemoglobin is more readily eluted through the cell membrane in the presence of acid than is fetal hemoglobin (HbF).

Procedure

• The maternal blood is fixed on a slide with ethanol (80%) and treated with a citrate phosphate buffer to remove the adult hemoglobin.

• After staining with hematoxylin and eosin, the fetal cells can readily be distinguished from the empty maternal cells.

The green marks are pointing to fetal HGB.

Screening for Rh Isoimmunization

Initial Steps

• Identify mother’s blood group in the first ANC visit.

• If Rh-negative patients → check father → If Rh neg, the fetus will be Rh neg → safe.

• If the father is Rh positive, his Rh genotype and ABO status should be determined.

• If the father is:

  • Homozygous for the D antigen → every fetus will be Rh positive.
  • Heterozygous → only half of his children will be positive.

Follow-Up for Rh-Negative Pregnancies

Monitoring and Testing

• If it is not possible to test the antigen status and zygosity of the father, it must be assumed that he is antigen positive.

• MATERNAL Rh-ANTIBODY TITER Anti-D antibody titers.

• Serial Ab titer gives + serial USS and + past ob Hx → guides management.

Follow-Up Methods

Cut‑off titer level: < 1:16 Z

• If the titer is < 1:16, repeat the test every 2–4 weeks. - insignificant
• When the titer rises to ≥ 1:16, a detailed assessment is warranted. - significant - maternal RH testing if exceeds - if parental negative ⇒ routine, positive ⇒ Amniocentesis for RHD antigen

Factors influencing the timing and method of invasive testing

1. Current clinical status of the fetus
2. Gestational age
3. Patient’s obstetric history

Note (ACOG): the titer reflects how many times maternal blood can be diluted while still detecting anti‑D antibodies.

Clinical tip: Titers are generally not useful for monitoring a patient with a history of a previous fetus affected by hemolytic disease.

Non-Invasive and Invasive Techniques

Non-invasive Invasive

1. Ultrasonography 1. Amniocentesis
2. Doppler velocimetry of MCA 2. Fetal blood sampling

Monthly Maternal Indirect Coombs Titre

Management Based on Titre Levels

• Exceeds Critical Titre
  • Paternal Rh Testing
    • If Rh Positive
      • Amniocentesis for RhD antigen status
        • Fetus RhD positive
          • Serial Amniocentesis
        • Fetus RH D Negative
          • Weekly MCA-PSV

            • 1.50 MOM

            • < 1.50 MOM - Cordocentesis or Deliver
    • If Rh-negative
      • Routine Care
• Below Critical Titre
  • repeat 2-4 wks

Ultrasonography

Role in Monitoring Fetal Condition

• To Establish The Correct Gestational Age.

• In Guiding Invasive Procedures And Monitoring Fetal Growth And Well-being.

• Ultrasonographic Parameters To determine Fetal Anemia: * Placental Thickness. * Umbilical Vein Diameter (increased). * Hepatic Size. * Splenic Size. * Polyhydramnios. * Fetal Hydrops (e.g., Ascites, Pleural Effusions, Skin Edema). * Blood velocity (increased).

Doppler Velocimetry of Middle Cerebral Artery (MCA)

Predicting Fetal Anemia

• Anemic fetus preserves oxygen delivery to the brain by increasing cerebral flow (sparing effect).

• For predicting fetal anemia.

• Predict the timing of intrauterine fetal transfusion.

Invasive Techniques for Diagnosis

Indications and Procedures

• Critical anti-D titer: A titer associated with a significant risk for fetal hydrops (Anti-d titer value between 8 and 32).

• Previous seriously affected fetus or infant.

Amniocentesis

Procedure and Interpretation

• Bilirubin in amniotic fluid decreases with advanced gestation.
• It derives from fetal pulmonary and tracheal effluents.
• Its level rises in correlation with fetal hemolysis.

Determination of Amniotic Fluid Bilirubin

• By the analysis of the change in optical density of amniotic fluid at 450 nm on the spectral absorption curve (delta od450).
• Procedures are undertaken at 10–15 days intervals until delivery data are plotted on a normative curve based upon gestational age.

Amniocentesis Procedure

Key Elements

Queenan Curve for Delta-OD 450 Values

Assessing Risk of Intrauterine Death

Interpretation Of Amniotic Fluid Bilirubin

Clinical Implications

• A falling curve: is reassuring (An unaffected or Rh D-negative fetus).

• A plateauing or rising curve: suggests active hemolysis (require close monitoring & may require fetal blood sampling &/or early delivery).

• A curve that reaches to or beyond the 80^th percentile of zone II on the Liley graph or enters the “intrauterine transfusion” zone of the Queenan curve necessitates investigation by fetal blood sampling.

Fetal Blood Sampling

Gold Standard for Detection of Fetal Anemia

• Is the gold standard for detection of fetal anemia.

• Reserved for cases with:

  1. With an increased MCA-PSV.
  2. Increased ∆OD 450.

• Complications:

  • Total Risk of Fetal Loss Rate 2.7%.
  • Bleeding from the puncture site in 23% to 53% of cases.
  • Bradycardia in 3.1% to 12%.
  • Fetal-maternal hemorrhage: occur in 65.5% if the placenta is anterior and 16.6% if the placenta is posterior.
  • Infection and abruptio placenta (rare).