Rh Rhesus Isoimmunization

CHUKWUMA I . ONYEIJE , M.D.ATLANTA PERINATAL ASSOCIATES

Rh (Rhesus) Isoimmunization:Perinatal Implications and

Management

A copy of this lecture can also be found at:

http://onyeije.net/present/rhdis

Objectives

Review TerminologyReview Major Blood Group AntigensReview Minor Blood group antigensOverview of Clinical ManagementDiscuss Prevention StrategiesQ&A

Rh DiseaseAlloimmunizationIsoimmunizationHDFNErythroblastosis

Fetalis

Confusing Terminology

Rh (Rhesus) Isoimmunization:

RED BLOOD CELLANTIGENS

AND ANTIBODIES.

Pathophysiology

INTRODUCTION:FOUR BLOOD TYPES ( A, B, AB, AND O)

EACH BLOOD TYPE IS ADDITIONALLY CLASSIFIED ACCORDING TO THE PRESENCE OR ABSENCE OF THE RH FACTOR

Rh Incompatibility

Occurs when there is a different Rh blood type between that of the pregnant mother (Rh negative) and that of the fetus (Rh positive)

Rh Incompatibility

Exposure to fetal

ANTIGENS causes the mother to produce

ANTIBODIES

The placenta usually acts as a barrier to fetal blood entering

the maternal circulation.

Fetal cells can enter the maternal circulation through a

“break” in the “placental barrier”.

Maternal production of Rhesus antibodies following introduction

of Rhesus positive blood

Maternal production of Rhesus antibodies following introduction

of Rhesus positive blood

Causes of RBC Transfer: “A break in the barrier”

Abortion/Ectopic Pregnancy

Partial molar pregnancy

Blighted ovumAntepartum bleedingProcedures

(amniocentesis, cordocentesis, CVS)

External versionPlatelet transfusionAbdominal traumaInadvertent

transfusion Rh+ blood

Postpartum (Rh+baby)

IMMUNIZED PREGNANCY

NON-IMMUNIZED PREGNANCY

Rh Incompatibility

Pathophysiology

After first antigenic exposure, memory B lymphocytes

recognize appearance of RBC’s containing the antigen in subsequent pregnancies

Pathophysiology- Fetal Events

Maternal antibodies cross the placenta & attach to fetal RBC’s- leading to RBC destruction

Sequestration by macrophages in fetal spleen (extravascular hemolysis) produces fetal anemia

METABOLISM OF BILIRUBIN:

JAUNDICE DOES NOT OCCUR BEFORE DELIVERY:

* Hemolysis/Anemia is basis of MCA-PSV

** Increased Bilirubuin is basis of Delta OD-450

*

*

WHAT’S HARMLESS?

WHAT’S DANGEROUS?

Antigen Nomenclature

CDE (Rhesus) System

Clinically ImportantIncludes c, C, D, e, ERh negative status indicates the absence of D antigen

87% of Caucasians carry the D antigen

Other Antibodies

Antigens such as A, P, Le (a), M, I, IH, and Sd (a) are innocuousMost are IgM

Lewis antibodies and cold agglutinins of I are prevalent but not clinically significant“Lewis Lives”

Antibodies Associated with HDFN

Anti-c, Anti-D, Anti-E, and Anti-Kell

Antibodies Associated with HDFN

RhoGAM has decreased HDFN caused by anti-D

Anti-D antibody is still MOST COMMON CAUSE of red cell isoimmunization

Minor RBC Antigens

Kell is most common of minor Responsible for 10% of cases of severe antibody-mediated anemia

Mechanism of anemia two-fold1. Hemolysis2. Suppression of

erythropoiesis**Transfuse women with Kell(-) blood**

Minor RBC Antigens

Duffy antigens Fy(a) and Fy(b)Only anti-Fy(a) antibody associated with HDFN- may range from mild to severe“Duffy Dies”

We treat sensitization to minor RBC antigens similar to those with Rh isoimmunization

Minor Antigens

MNS system = M, N, S, s, U antigens

Anti-M and anti-N naturally occurring- no clinical significance

Anti-S, anti-s, and anti-U antibodies ~ mild to severe HDFN

Clinical Management

Routine blood type screenRepeat Ab screen at 24-28 weeks for Rh negative women PRIOR to receiving RhoGAM

If Ab screen is (+), identify antibody and potential for HDFN

Clinical Management For Positive Antibody Screen

Determine risk factors for isoimmunization Past pregnancies Transfusions Shared needles

Determine father’s RBC antigen status and zygosity

If paternity unknown or father is (+) for antigen, fetus is at RISK

Clinical Management For Positive Antibody Screen

Obtain antibody titer

Consider invasive testing at titer of 1:32 or greater by indirect Coombs (1:16 most often used)

If AB titer remains below critical titer…Invasive testing can be deferredEvaluate serial Ab titers

Serial titers are NOT necessary before 18-20 weeks

If critical titer noted at first visit, amnio for delta OD450 at 22-24 weeks

Clinical Management For Positive Antibody Screen

Clinical Management Fetal Testing

Obtain amniocytes to determine fetal blood type

When father is heterozygous for the antigen responsible for alloimmunization

When paternal status is unknownMCA-PSV can be used as early as 18 weeks~ if greater than 1.5 MoM, consider fetal blood sampling

Normal and Abnormal MCA Dopplers

The Middle Cerebral Artery

Should be examined close to its origin in the internal carotid artery.

The angle of the ultrasound beam and the direction of blood flow should be zero degrees.

The risk of anemia is highest in fetuses with a peak systolic velocity of 1.5 times the median or higher.

MCA Doppler and Fetal Anemia

Fetuses with anemia show an increased peak velocity of systolic blood flow in the middle cerebral artery (MCA)

MCA Doppler is useful in the determination of fetal anemia in Rh-isoimmunized pregnancies

MCA Doppler is also used to follow fetal response to intrauterine transfusion and to assist in timing subsequent transfusions.

MCA Doppler and Fetal Anemia

Method: MCA closest to the maternal skin should be measured using

a minimal angle of insonation The Doppler gate is placed over the vessel as it bifurcates

from the carotid siphon.

Serial MCA Doppler studies can be used to generate a curve that plots MCA peak systolic velocity as a function of gestational age.

After 35 weeks' gestation, accuracy in determining MCA PSV appears to decrease; therefore, at this gestational age amniocentesis for deltaOD450 is indicated.

Clinical Management (cont)

Perform serial amniocenteses to measure delta OD450

ANDPlot values on Liley Curve

“Belt and Suspenders” Approach

Delta OD450Spectral analysis of amniotic fluid at 450 nm measures change in OD

Measures the level of bilirubin and predicts severity of hemolytic disease after 27 weeks

Delivery or intrauterine transfusion if delta OD450 falls into zone III or upper zone II

Rh Isoimmunized Pregnancy Worksheet

Cordocentesis

Gold standard for detection of fetal anemia

Complications2.7% total risk of fetal lossReserved for patients with increased MCA-PSV or delta OD450

Advantages of MCA-PSV

Non-invasiveNO risk for worsening isoimmunization

Utility with alloantibodies other than Rh-D, including anti-Kell antibodies

Caution Regarding MCA-PSV

From: http://youtu.be/FGUFC39Bgu0

Review of Management for Rh Isoimmunization

Monthly indirect coombs titer (in first sensitized pregnancy)

If critical titer reached, determine paternal and fetal antigen status

Amniocentesis and delta OD450 OR MCA-PSV

** For 2nd or greater sensitized pregnancy, initiate amnio or MCA at 18-20 weeks**

Prevention (cont)

Give 300 mcg dose within 72 hrs of delivery to unsensitized Rh (-) women (Rh positive infant)

ACOG: 300 mcg at 28 weeks UNLESS father known to be Rh (-)

PreventionTest for excessive fetal-maternal hemorrhage after blunt trauma, abruption, cordocentesis, and bleeding assoc. with previaKleihauer Betke

Give RhoGAM for partial molar pregnancy, SAB, TAB, ectopic, chorionic villus sampling, amniocentesis, external version

SUMMARY

Remember the instances in which to consider RhoGAM

SAB, TAB, threatened AB (controversial), ectopic, previa/bleeding, abruption, partial molar, CVS, blunt trauma, cordocentesis

Clinically important antibodies: Anti-c, Anti-D, Anti-E, and Anti-Kell, Rarely Anti-Duffy Fy(a)

Usually not associated with severe HDFN: , ABO incompatibilities, Anti-Duffy(Fy-b)

antibodies, (Duffy Fy-a causes mild to severe HDFN), Anti-A, Anti-P, Anti-M, Anti-I, Anti-IH, Anti-Sd(a)

SUMMARY

Anti-D still most common cause of red cell alloimmunization, despite RhoGAM

Kell = most common minor antigenCritical titer most often used is 1:16 by

indirect CoombsAmnio with delta OD450 & MCA-PSVAntibody screens and indications for

RhoGAM

References

1. Gabbe Obstetrics – Normal and Problem Pregnancies, 4th edition.2. Creasy R., Resnik R., Iams J., Maternal Fetal Medicine Principles and

Practice, 5th edition.3. ACOG Compendium 20054. Harkness U., Spinnato J., Prevention and Management of RhD

isoimmunization. Clinics in Perinatology, Dec 2004 31:4.5. Pereira L., Jenkins T., Conventional management of maternal red cell

alloimmunization compared with management by Doppler assessment of MCA-PSV. American Journal of Obstetrics and Gynecology, Oct 2003 189:4.

6. Cohen D., Hemolytic disease of the newborn: RBC alloantibodies in pregnancy and associated serologic issues. Up to Date, Oct 2004.

7. Barss V., Moise K., Significance of minor red blood cell antibodies during pregnancy. Up to Date, Apr 2005.

Online resources: www.austincc.edu/mlt/bb/bb_HDN.ppt http://www.perinatology.com/Archive/Isoimmunization.htm http://emedicine.medscape.com/article/273995-overview http://www.nlm.nih.gov/medlineplus/ency/article/001600.htm

Kleihauer-Betke Test

% fetal RBC in maternal circulationFetal erythrocytes contain Hbg F which is

more resistant to acid elution than HbgA so after exposure to acid, only fetal cells remain & can be identified with stain

1/1000 deliveries result in fetal hemorrhage > 30ml

Risk factors only identify 50%

Kleihauer Calculations

Fetal red cells = MBV X maternal Hct X % fetal cells in KB

newborn Hct

MBV – maternal blood volume (usually 5000ml)

Fetal cells X 2 = whole blood