Management of the Fetus and Newborn - Part 2

Focus: Management of the fetus and newborn, specifically blood bank testing during postnatal care.
Objective: Discussing actions taken immediately after birth for both mother and baby.

Cord blood is collected from all newborns at the time of birth.
Collection methods:
- Usually collected using a syringe.
- Typically placed in either:
- Big red top tubes (serum tubes used in phlebotomy).
- Clear screw cap tubes used for collecting spinal fluid.
Purpose: Samples are sent to the blood bank for analysis.
Testing on cord blood is contingent on a physician's order.

Initial tests conducted:
- Cord blood screen: evaluates blood type and Direct Antiglobulin Test (DAT).
- ABO and Rh typing to determine if the infant is Rh negative or positive.
Note: No reverse type is performed initially because detecting maternal antibodies can lead to confusion; reverse typing can be conducted when the infant is older.
Importance: Cord blood helps confirm or deny possible hemolytic disease of the fetus and newborn (HDFN).
Direct Antiglobulin Test (DAT):
- Essential for diagnosing HDFN.
- Testing reagents must contain anti-IgG.
- A positive result indicates antibody coating on infant's red cells.
Distinction from adult DAT:
- In adults, further determination is needed to check for IgG or complement.
- Positive or negative results on cord blood indicate completion of testing requirements unless further elution tests are requested by a physician.

Determining the need for RhoGAM administration or possible transfusion if the infant is anemic.
Importance of testing for antibodies if transfusion is possible.
Wharton's Jelly:
- A gelatinous substance in the umbilical cord.
- Must be washed away from cord blood to avoid false positive results, such as a falsely negative Rh typing which could occur if the baby had intrauterine transfusions.

Strong reactions do not correlate directly to disease severity.
Example: A positive DAT with a negative antibody screen could be an ABO-related issue in HDFN.
Elution tests are not usually recommended unless fetal demise causes remain unknown or there are clinically significant antibodies.

When is it done?
- Required if the infant is anemic.
Purpose of exchange transfusion:
- Correct anemia without increasing blood volume.
- Remove elevated unconjugated bilirubin levels.
- Prevent pathological conditions like kernicterus.
Unconjugated bilirubin:
- Waste product from hemoglobin breakdown, not properly excreted due to immature liver or prematurity.
Steps in exchange transfusion:
- Whole blood or an equivalent is used to replace the infant's circulating blood.
- Maternal antibodies and incompatible red cells are replaced with fresh donor cells to prevent anemia and high bilirubin levels.
Considerations:
- Target hematocrit should be between 45% and 60%.
- Packed red blood cells used must be:
- Less than seven days old to minimize storage lesions and high potassium levels.
- Negative for hemoglobin S to prevent sickle cell complications.
- Leukocyte reduced and/or CMV negative to minimize risks of developmental issues.
- Cross-match compatibility with maternal plasma is required.
- Important to note: once blood is spiked, it must be used within 24 hours due to expiration.

RhoGAM: Rh immunoglobulin to prevent Rh immunization in Rh-negative mothers.
Contains IgG anti-D, effective only against D antigen.
Important immunological note: Does not protect against other antigens (like anti big C, little c, etc.).
Criteria for RhoGAM administration:
- Mother must be D negative and infant D positive (or weak D positive).
- Administered within 72 hours after delivery of an Rh-positive infant.
Timing and dosing:
- Typically given at 28 weeks of gestation to D-negative mothers.
- Additional doses may be given during pregnancy for invasive procedures (like amniocentesis).
- If the baby is Rh negative, no administration of RhoGAM is required.
RhoGAM's effectiveness is based on the mechanism believed to interfere with antigen recognition and immunization phases.

FMH screen (also known as rosette test) determines RhoGAM dosage.
Must be done post-delivery using maternal blood drawn within an hour for accuracy.
Expected outcome:
- Positive result indicates potential fetal bleeding into the maternal circulation, requiring further testing.
Klyhauer-Betke stain:
- Used when FMH screen is positive to quantify fetal hemorrhage.
- Fetal cells maintain a hot pink appearance; maternal cells appear pale after acid treatment.
- A count of 2,000 cells determines the proportion of fetal versus maternal cells to calculate the required RhoGAM dose.
- Factor of 5,000 is used for blood volume calculation; result is divided by 30 (as one vial of RhoGAM suppresses a 30 mL bleed).
Newer method: Flow cytometry to detect fetal blood cells using monoclonal antibodies targeting D-positive antigens.

Patient: 32-year-old female, first pregnancy.
Type and Screen Results: Rh negative, negative antibody screen.
- Requires RhoGAM at 28 weeks.
Delivery: Baby boy born, Rh positive, positive DAT.
- Next step: perform FMH screen.
FMH Screen Result: Positive
- Next test: Klyhauer-Betke stain.
Results: 35 fetal cells counted out of 2,000.
- Calculation for RhoGAM: 35/2000 x 5000 gives fetal bleed, result divided by 30 = 4 vials of RhoGAM required.

Patient: Barb Dwyer, third child.
Type and Screen Results: Rh negative, A negative, negative antibody screen.
- Requires RhoGAM at 28 weeks.
Delivery: Baby girl born, Rh positive, negative DAT.
- Next step: perform FMH screen.
FMH Screen Result: Negative
- Conclusion: one vial of RhoGAM is required to cover potential maternal-fetal bleeding.

Comprehensive understanding of postnatal blood bank testing is critical in ensuring the health of both mother and newborn, especially concerning the management of Rh incompatibility and hemolytic diseases.