Prevention of Rh Alloimmunization

Question 1

Reasons you might have commingling of blood between mom and fetus

Answer 1

spontaneously
miscarriage
ectopic pregnancy
ante natal bleeding
ECV
delivery
amniocentesis
cvs

Question 2

how do problems happen with alloimmunication

Answer 2

• patient makes antibodies
• antibodies cross the placenta
• these destroy fetal RBCs, causing various degrees of fetal anemia
• 0.1cc blood commingling is enough to create a problem

Question 3

How do you prevent problems

Answer 3

• Give Anti-D antibody
• 300ug at 28w (covers silent spontaneous maternal- fetal transfusions
• during delivery if baby is Rh positive, then KB test or flow cytometry should be done to assess for how much rhogam is needed

Question 4

if Rh neg over is found to have antibodies…

Answer 4

• still should get rhogam if the anti-D immunoglobulin. are deemed to be passive consequent due to recent administration of rhogam
• if deemed to be actively generated (natural immune mediate response), administration will not be effective

Question 5

FOB status

Answer 5

• 3% non-paternity

- therefore all women should be treated regardless of paternal status

Question 6

Weak D

Answer 6

= partial expression of D antigen

• can still develop antiD antibodies to that portion of the D antigen which they do NOT possess, they can still cause iso-immunization of an Rh- positive baby
• these women should be treated like they are negative
• they should get Rhogam
• if these pt’s donate blood, they are treated at Rh+ blood (cause they have some expression)

Question 7

threatened AB <12w

Answer 7

• lack of data, no recommendation offered

- some give 50 ug dose

Question 8

• molar pregnancy

Answer 8

• yes should get rhogam

Question 9

surgical or medical abortion <12w

surgical or medical ectopic pregnancy

Answer 9

50 ug of rhogam
(300 ug after 12w)
Goes up because increasing RBC volume

Question 10

trauma

Answer 10

should give Rhogam and KB test to determine how much

Question 11

ante natal hemorrhage

Answer 11

KB to determine how much rhogam

Question 12

screening recommended at

Answer 12

28w

Question 13

rhogam is good for

Answer 13

3 weeks

Question 14

If doesn’t get it pp

Answer 14

still give it at 28d follow up appointment, may still have benefit

Question 15

Rh basic screening program

Answer 15

• non-sensitized women should get anti-D immunoglobulin at 28w and within 72h of birth if neonate confirmed positive (KB test needed to determine how much

Question 16

Antibodies that cause fetal hemolysis

• Marked
• Mild

Answer 16

Marked

• Kell (K1)
• RhD
• Rhc (small c)

Mild

• Duffy
• Kidd
• RhC
• RhE
• Rhe

Question 17

Amount of Rhogam needed

Answer 17

• 300 mcg for sig bleeding or invasive procedure (72h-28d)
• 300 mcg covers 30 ml fetal whole blood, 15 of RBC
• Give 300 mcg at 28 ppx
• delivery give 300, KB to determine if need more (0.3% deliveries)
• If protocols not followed, 17% will get alloimmunized (not 100%)

Question 18

Management of Alloimmunnzation in pregnancy

First pregnancy/Current

Answer 18

First pregnancy = mild disease

Follow maternal titers if titer is 8 or less

• – <24w, monthly titers
• – >24w, q2w titers

Critical titer: 8-32

• – risk of hydrops
• – begin MCA dopplers (looking for fetal anemia)
• – note Kell titers not predictive of fetal status

MCA dopplers protocol

• q1-2w
• MCA > 1.5 MoM – PUBS, possible IUT
• IUT threshold often fetal Hct 30%

Question 19

Paternity and alloimmunization

Answer 19

Generally not trusted

FOB positive (hetero)

• 50% chance fetus at risk for hemolyic disease
• Can test fetus through sfDNA (if RhD)
• Amnio for all other types

FOB positive (homo)

• 100% change fetus at risk for hemolytic disease
• Needs MCA doppplers

Question 20

Alloimmunization

Second pregnancy

Answer 20

Titers nto predictive

FOB hetero
- Get fetal status (cfDNA if RhD, amnio otherwise)

FOB homo
- MCA dopplers start at 18w