Rh Factor ISOIMMUNIZATION Associate Professor Iolanda Blidaru, MD, PhD.

Rh Factor ISOIMMUNIZATION

• Associate Professor Iolanda Blidaru, MD, PhD

INTRODUCTION

ANTIGEN >400 Agglutinogens on the cell

membrane

R.B.C. Plasma

ANTIBODY

Natural & Immune Agglutinins/ Isoantibodies

Antigen-Antobody reaction on the cell surface Hemolysis

INTRODUCTION

• controlled by genes at chromosomal loci• appeared by 40 days of i.u. life• unchanged till death• present in tissues and tissue fluidsBlood group system - a group of antigens

controlled by a locus having a variable no. of allele genes.

Antigens

INTRODUCTION

• > 15 recognised blood group systems ABO, Rh, Kell, Duffy, MNS, P, Lewis,

Lutheran, Xg, Li, Yt, Public antigens & Private antigens.

• Blood-type means individual antigen phenotype which is the serological expression of the inherited genes.

• Most of these blood group antigens have been found to be associated with hemolytic disease.

• ABO & Rh account for 98%.

Antigens

INTRODUCTION

Alloantibodies / Agglutinins

Pre-existentIgM

Iso-antibodiesIgG

Formed in response to foreign R.B.C. or soluble blood group substances

Antibodies

INTRODUCTION

• Formed against most of the major group antigens and present in individuals.

• IgM type.

• Do not cross placenta.

• React poorly at body temperature (except anti-A and anti-B), but agglutinate erythrocytes at 5-20°C

Pre-existent (natural) Antibodies

INTRODUCTION

• The isoantibodies are IgG.

• Best react at body temperature

• Cross the placenta readily.

• Most Ab are complement binding.

Iso-Antibodies

Immunology of Rhesus Blood Group System

• First demonstrated by testing human blood with rabit anti sera against RBC of Rhesus monkey → classifying into Rh negative / Rh positive.

• The genotype is determined by the inheritance of 5 closely linked allelic genes situated on the short arm of chromosome 1, named as D,C,c,E,e (Fisher-Race).

• No ”d” → absence of D• The foetus inherits one gene from each group as

a haplotype such as sets of cDe, CDE, etc from each parent.

Immunology of Rhesus Blood Group System• 12 sets of combinations and 78

genotypes are possible. • For clinical and all practical purposes it

is enough to know whether one is Rh POSITIVE or NEGATIVE against anti D sera.

• The antigenic expressions of these genes are the coresponding antigens, consisting of C/c, D/d, E/e.

• The antigenic determinants form an intrinsic part of the red cell membrane protein structure.

Immunology of Rhesus Blood Group System• C/c and E/e are weak antigens.• ‘D’ is the most immunogenic in the Rh

system.• There is a rare type of Rh negative called

Rh null who lack all known Rh antigens.• ‘D’ antigen has no natural antibody.• A single transfusion of Rh+ blood to a

Rh– person has a 50% chance of forming anti Rh D antibodies.

Incidence of Rhesus Blood Group System

Incidence of Rh negative varies in different races and ethnic groups• Mongoloids = nil • Chinese, Japanese = 1-2%• Indians = 5% • Africans = 5-8%• Causcasians = 15-17%• Basques = 30-35%

Pathogenesis Of Rh Iso-immunization

Rh Negative Women Man Rh positive (Homo/Hetero)

Fetus Rh Neg Fetus No problem

Rh positive Fetus

Rh+ RBCs enter maternal circulation

Mother previously sensitized Secondary immune response

Iso-antibody (IgG) (

Non sensitized mother Primary immune response

Fetus unaffected

1st baby usually escapes. Mother gets sensitised?

Fetus

Haemolysis

Pathogenesis Of Rh Iso-immunization

• Chances of feto-maternal hemorrhage / passage are only 5% in 1st trimester but 47% in 3rd trimester; many conditions can increase the risk.

• Chances of primary sensitization during 1st pregnancy is only 1-2%, but 10-15% of patients may become sensitized after delivery.

• ABO incompatibility and Rh non-responder status may protect.

• Amount of antibodies that enter the fetal circulation will determine the degree of haemolysis.

Pathology Of Erythroblastosis fetalis

HAEMOLYSIS IN UTEROAFTER BIRTH

BILLIRUBIN

ANAEMIA

MAT. LIV → NO EFFECT

HEPATIC

ERYTHROPOIESIS & DYSFUNCTION

PORTAL & UMBILICAL VEIN

HYPERTENSION, HEART FAILURE, HYDROPS FETALIS

BIRTH OF AN AFFECTED INFANT - Wide spectrum of presentations. Rapid deterioration of the infant after birth. May continue for few days to few months.

Jaundice

Kernicterus Hepatic Failure

DEATH

ERYTHROBLASTOSIS FETALIS

INTRAUTERINE DEATH

Antenatal Diagnosis Of Rh Iso-immunization

• the history and physical exam. • the maternal and paternal Rh blood type• anti-Rh Ab screen (monthly after 20-th week) –

by indirect Coombs test; if positive as 1/8-1/32, there is needed further assessment

• ultrasound exams• fetal anemia and hyperbilirubinemia – by

ultrasound guided amniocentesis

→ spectrophotometry of amnionic fluid (Liley chart)

→ CORDOCENTESIS – fetal blood tests

Antenatal Diagnosis Of Rh Iso-immunization - ultrasound exams


• Liley chart


Postnatal Diagnosis Of Rh Iso-immunization

Hemolytic disease of the newborn• Hemolytic anemia (Hb = 13-14g%;

bilirubin < 3.5mg%) • Icterus gravis neonatorum (Hb = 7-

12g%; bilirubin > 10mg%) • Kernicterus (bilirubin > 18mg%) • Hydrops fetalis (Hb < 7-12g%;

bilirubin > 10mg%)


Hydrops fetalis

Hydrops fetalis


Laboratory tests (newborn)• ABO and Rh blood group test• Hb and Ht• Reticulocyte count• Bilirubin level• Direct Coombs test

Prevention of Rh Iso-immunization

• Premarital counseling.

• Blood grouping for every woman,

before 1st pregnancy.

• Proper management of unsensitised

Rh negative pregnancies.


Blood typing at 1-st visit, If negative → husband’s typing. Anti-Rh Ab screen (indirect Coomb’s test) of Rh–negative

mother. At about 28 weeks – negative → 300μg anti D

immunoglobulin. In abortion, ectopic pregnancy, abruption of placenta,

placenta praevia, molar pregnancy, abdominal trauma, chorionic villi sampling, amniocentesis = foetal-maternal hemorrhage → 150-300μg anti D

At birth- cord blood for ABO and Rh typing → Baby Rh positive → 300μg anti D within 72 hours of delivery

Prevention of Rh Iso-immunizationIn case of large fetal-maternal hemorrhage:

1.the Kleihauer-Betke test estimates the amount of fetal blood in circulation

2.the indirect Coombs test3.an additional dose of anti-D, if

needed

The Kleihauer-Betke test


Errors - Causes of sensitization • Misinterpretation of maternal Rh type• Rh+ blood transfusion• Unprotected pregnancy and labour• Inadequate dose / improper use of

IgG on previous occasions• Immunization to cross-reacting

antigen

Management of Rh Iso-immunized PregnancyANTEPARTUM• Careful planning during antepartum,

intrapartum and neonatal period• Known repeated maternal anti-D Ab titer • Intrauterine fetal monitoring with repeated

US examinations, cordocentesis & fetal blood sampling / amniocentesis, the measurement of the fetal middle cerebral artery peak velocity (Doppler)

Management of Iso-immunized Pregnancy

• Fetus Rh Positive + anemia • Intrauterine transfusion of Rh-

negative blood in selected cases• Planned preterm delivery any time

after 34 weeks or as soon as the lung maturity is documented by inducing the labor or cesarean section (for the severely affected fetuses)

Management of Iso-immunized Pregnancy

POSTPARTUM Management of the infant

• Monitoring up to 8 weeks• Exchange-transfusion in the newborn in

the umbilical vein• Phototherapy• In cases of severely sensitized women,

consider medical termination of pregnancy and sterilization.

Rh Factor ISOIMMUNIZATION Associate Professor Iolanda Blidaru, MD, PhD.

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