RH ISOIMMUNISATION Flashcards
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RH ISOIMMUNISATION
Rhesus (Rh) alloimmunization (isoimmunization) is an immunologic disorder that occurs in a pregnant, Rhnegative woman who is carrying an Rh-positive fetus.
Defined as a production of immune Abs in an individual in response to foreign red cell antigen derived from
another individual of the same species provided, the first one lacks the antigen.
Rhesus factor
Rh system is composed of 5 different antigens
C, E, c, e and D antigen (are the most frequently associated with isoimmunisation)
D antigen is the most potent and accounts for almost all damages (95%) due to Rh blood groups,
Its presence or absence denotes an individual to be Rh-positive or Rh-ve respectively
Rh positive (Rh+): patient has D antigen on red blood cells (RBCs)
Rh negative (Rh -): patient lacks D antigen on RBC (gene deletion)
Genotype is either Dd (D only in one set, called heterozygous-35%) or DD (D on both sets of antigens- called
homozygous-65%)
Heterozygous persons, are always classified as Rh-positive because D is dominant to d
Homozygous or heterozygous father determines whether all fetuses will be affected
For homozygous fathers, all his genes will be incompatible
with a Rh-negative mother and so all children will be Rhpositive (Dd) and may be affected by hemolytic disease
Method of Rh- isoimmunisation
Occurs in 2 stages:
(1) Sensitization
(2) Immunization.
When RhD -ve pts are exposed to the RhD antigen, they may become sensitized.
After that the individual become immunized by producing Abs against the RhD Ags
Causes of Sensitization in Rh- isoimmunisation
sensitization are caused by a
1. Placental leak of fetal RBCs into maternal circulation (fetomaternal hemorrhage) during pregnancy.
Normally, the fetal red cells containing the Rh antigen rarely enter the maternal circulation.
Immunization is unlikely to occur unless at least 0.1 mL of fetal blood enters the maternal circulation & only
about 17% of Rh -ve women will be “at risk” of being alloimmunized by a single Rh-incompatible pregnancy
Rh Ag rarely enter maternal circulation but risk of fetomaternal bleed is present in following
conditions:
a) Miscarriage
b) MTP
c) Genetic amniocentesis
d) Ectopic pregnancy
e) Hydatidiform mole
f) CVS
g) Cordocentesis
h) Antepartum fetomaternal hemorrhage- placenta previa and placental abruption
i) IUFD
j) External cephalic version
k) Abdominal trauma
l) Delivery of a Rh-D +ve infant to a Rh -ve mother.
2. Transfusion of mismatched blood:
In Rh group, no naturally occurring Ab pre-exist as in ABO group incompatibility
And so no immediate reaction but the red cells carrying the Rh antigen sensitize immunologically competent
cells in the body, provided the amount is sufficiently large.
Following a subsequent exposure to Ag, cells are stimulated to produce more specific anti-D antibody.
The women may suffer a severe hemolytic reaction to the subsequent mismatched transfusion.
3. “Grandmother” theory- suggests that an RhD _ve woman may been sensitized from birth by receiving enough
RhD +ve cells from her mother during her own delivery (i.e., a maternal-fetal hemorrhage) to produce an
antibody response.
Immunization in Rh- isoimmunisation
Ab production is related to reticuloendothelial system responsiveness and also to amount of Rh Ag liberated, to
the number of red cells that entered the maternal blood.
Immunization in a 1st pregnancy is unlikely and detectable Abs usually develop after 6 months following larger
volume of feto-maternal bleed.
For fetomaternal bleed < 0.1 mL, Ab may not be detected until boosted by further Rh stimulus.
Abs once formed remain throughout life.
Two types of antibodies are formed:
a. IgM- 1
st to appear in maternal circulation. IgM are larger molecules and cannot pass via the placental
barrier and is not harmful to the fetus.
b. IgG- called incomplete or blocking Ab. It’s a small molecule, appears at a later period than does IgM Ab
and can cross placental barrier and cause damage to fetus
Pathophysiology of Rh- isoimmunisation
In general, 2 exposures to RhD Ag are required to produce any significant
sensitization, unless 1
st exposure is massive.
1
st exposure leads to primary sensitization, and production of IgM Abs
Whereas 2
nd exposure causes an anamnestic response leading to the rapid production of IgG antibodies.
If the fetus has RhD Ag, these Abs will cross the placenta & attach to surface Ags on the fetal RBCs,
Affected rbcs are rapidly haemolysed by reticuloendothelial system (spleen) & complement mediated pathways
Mild haemolysis, is compensated by increasing rate of erythropoiesis-Anaemia in 1st 2 wks of life- Hb 14-
18gm%, bilirubin >5mg% with reticulocytosis
Severe haemolysis can lead to profound fetal anemia, resulting in various types of fetal hemolytic diseases,
loosely termed as erythroblastosis fetalis
- They are large number of nucleated cells in fetal peripheral blood in response to anemia and also cause;
a. Extramedullary hematopoiesis Hepatosplenomegaly
b. Portal hypertension,
c. Hypoalbuminemia,
d. Hyperbilirubinemia severe Jaundice with bilirubin > 10gm%
e. Heart failure (hydrops fetalis) anemic heart failure oedema, ascites, pleural effusion
f. Intrauterine fetal death.
g. High bilirubin levels can damage basal ganglia and lead to neonatal encephalopathy and kernicterus
cerebral palsy and sensorineural deafness
how to To prevent or minimize fetomaternal bleed in rh isoimmunisation
Precautions during cesarean section: To prevent blood spilling into the peritoneal cavity
Manual removal of placenta should not be done as a routine.
Prophylactic ergometrine with the delivery of the anterior shoulder should preferably be withheld, as it may
facilitate more fetoplacental bleed.
Amniocentesis should be done after sonographic localization of the placenta to prevent its injury.
Forcible attempt to perform external version under anesthesia should be avoided.
Manual removal of placenta should be done gently.
To refrain from abdominal palpation as far as possible in abruptio placentae.
AVOID transfusing Rh-positive blood to Rh-negative female from her birth until menopause
Manifestations of the hemolytic disease in rh isoimmunisation
a. Hydrops fetalis- most serious form of Rh hemolytic disease
b. Icterus gravis neonatorum
c. Congenital anemia of the newborn
hydrops fetalis
. Hydrops fetalis- most serious form of Rh hemolytic disease
Hydrops fetalis is fluid accumulation in 2 or more extravascular compartments; i. Pericardial effusion ii.
Pleural effusion).
Excessive haemolysis of fetal rbc leads to severe anemia, tissue anoxemia & metabolic acidosis.
That adversely affect the fetal heart, brain and placenta.
Placental tissue become hyperplasic in an effort to increase transfer of O2.
Fetal anoxemia, damage the liver leading to hypoproteinemia (↓oncotic pressure) responsible for anasarca
(hydrops fetalis), ascites and hydrothorax
Fetal death occurs sooner or later due to cardiac failure- either FSB or MSB and even NND soon after
Cardiac failure is due to; (i) High output failure secondary to anemia
(ii) Decreased oxygen delivery to myocardium
If a woman has a H/O fetal hydrops in a previous pregn, risk of hydrops with a subsequent pregnancy is about 90%.
Dx of hydrops fetalis
Rh-negative mother
a. Serum Rh-antibody
b. Polyhydramnios may be present
c. Previous H/O fetal hemolytic diseases
d. Real time Sonography (combined with pulse Doppler)- to detect edema in the skin,
scalp, pleural or pericardial effusion, placentomegally and echogenic bowel
e. Straight abd X-Ray- show fetus in “Bhudda” position with halo around
the head due to scalp oedema
At birth
f. Baby is pale and has ascites with hepatosplenomegally
g. Large pale placenta,oedematous and oozing fluid
Icterus gravis neonatorum
Clinical entity due to lesser form of fetal hemolysis.
Baby is born without jaundice but develops it within 24 hours of birth.
In-utero, haemolysed fetal rbcs liberates unconjugated bilirubin mostly excreted via the placenta into the
maternal system & some bilirubin enters liquor from fetal lung, skin or across placental surface or cord,
preventing onset of jaundice.
Soon after birth and umbilical cord is clamped, bilirubin increases and baby becomes jaundiced.
And liver is unable to conjugate the excessive bilirubin to make it soluble and nontoxic.
Bilirubin at critical level of 20 mg per 100 mL (340 micromol/L- normal 30 micromol/L), crosses bloodbrain barrier to damage basal nuclei of the brain permanently causing kernicterus – leading to cerebral
palsy and sensorineural deafness
Congenital anemia of the newborn in rh isoimmunisation
Mild form of Rh isoimmunisation when hemolysis is going on slowly
Anemia develops slowly within 1st few weeks of life, & jaundice is not usually evident.
RBCs haemolysis continues up to 6 wks after Abs are not available
Liver and spleen are , the sites of extramedullary erythropoiesis
Effects of Rh incompatibility on the mother
Rh incompatibility impact mainly falls on the baby.
But somewhat may also affect the mother by increasing incidence of;
a) Pre-eclampsia
b) Polyhydramnios
c) Big size baby with its hazards
d) Hypofibrinogenemia due to prolonged retention of a demised fetus
e) PPH due to big placenta and blood coagulopathy;
f) ‘Maternal syndrome’- salient features are generalized edema, proteinuria and pruritus
due to cholestasis are ominous features indicating imminent IUFD
Antenatal investigations of Rh-negative mothers
- Blood for Rh and ABO grouping
- For Rh-negative women, do Rh grouping for husband
- Husband Rh +ve - indirect Coombs’ test- to detect IgG Ab titre
- Detecting Fetomaternal Hemorrhage with Kleihauer-Betke test
- Amniocentesis and bilirubin estimation in amniotic fluid by spectrophotometry
- Cordocentesis
indirect Coombs’ test of rh neg mother with rh pos husband
Result may be:
A. Titre 1:8 or less arrange for Anti D
B. Titre 1:16 or more arrange for amniocentesis
Also determine husband’s Genotype- If homozygous, likely fetus is affected but if heterozygous, fetus 50%
chances of being affected.
Antibody detection in Rh –ve women: Maternal anti-D Ab titer is used as a screening tool to estimate
severity of fetal hemolysis in Rh disease.
Also helps guide decision making regarding initiation of testing procedures (e.g., MCA Doppler studies and
percutaneous umbilical blood sampling).
a. Primigravida If IgG Ab titre is negative at 12th week, repeat at 28th and 36th week
b. Multigravida to be repeated at monthly intervals from 24 weeks onwards.
c. Fetal Rh status by:
i. PCR for fetal DNA and genotyping using maternal plasma in 1st trimester.
ii. Amniocentesis or chorionic villi in 2
nd trimester and fetal RhD genotyping using amniocytes.
iii. Weekly quantitative estimation of IgG antibody- marked sudden rise in titre is suggestive of fetal
affection e.g., from 1: 8 to 1: 256
Kleihauer-Betke test
Kleihauer-Betke test- based on the fact that adult Hb is eluted more readily via the cell membrane in presence
of acid than is fetal Hb
Fix maternal blood on a slide with ethanol (80%) & treat with a citrate phosphate buffer to remove adult Hb.
Then staining with hematoxylin and eosin, fetal cells can readily be distinguished from the maternal cells.
Count all cells.
Determine % of fetal cells present on slide & estimate extent of fetomaternal hemorrhage (in mL of whole
blood) using the following equation:
% of fetal cells × 5000 (estimated maternal blood volume in mLs)
E.g., if Kleihauer-Betke is 0.2%, then estimated volume of fetal blood in maternal circulation would be
0.002 × 5000, or 10 mL of fetal whole blood
indications for Amniocentesis and bilirubin estimation in amniotic fluid by spectrophotometry
(1) High maternal antibody titre > 1: 8
(2) Previous history of IUFD or marked neonatal jaundice
(3) Father is heterozygous to determine if fetus is affected or not.
(4) Detection of lung maturity
Antenatal assessment of fetal well-being in rh neg mother
- Serial ultrasonography - detect hydrops fetalis and anaemia.
Possible features: polyhydramnios, placental thickness >4 cm, pericardial or pleural
effusion, echogenic bowel, dilatation of cardiac chambers and enlargement of spleen
and liver
Doppler ultrasound: Peak flow velocity in fetal middle cerebral artery, umbilical artery, ductus venosus aid
predict fetal anemia and acidosis. Value >1.5 multiples of median (MOMs) for corresponding GA, predicts
moderate to sev fetal anemia
Percutaneous umbilical blood sampling: If there is ultrasonic evidence of fetal hydrops, or if MCA peak systolic
velocity is >1.5 multiples of the median for GA, moderate to severe fetal
anemia may be present and so an indication for fetal bld sampling if the fetus
is at < 35 wks’ gestation.
PUBS allow measurement of fetal Hb, Hct, bld gases, pH & bilirubin levels
If fetal hct is < 30, or > 2 standard deviations below mean for GA,
intrauterine transfusion is indicated. - Cardiotocography- sinusoidal & decelerative pattern are observed in an
affected fetus. - Cordocentesis- done when ∆OD450 is elevated or elevated peak MCA Doppler
velocities (>1.5 MOM)
Cordocentesis indications
indications:
a. In place of amniocentesis if it needed before 20 weeks.
b. For intrauterine fetal transfusion (in high zone results and immature fetus)
c. Cordocentesis also helps to detect fetal blood type, hematocrit, DCT and total
bilirubin level. Fetal hematocrit value <15% is associated with hydrops
predictions from Amniocentesis and bilirubin estimation in amniotic fluid by spectrophotometry
Liley’s zone I (low zone): fetus is unlikely affected & continue pregn to term.
Liley’s zone II (mid zone): Repeat amniocentesis by 2 weeks → value upward
→ cordocentesis → hematocrit < 30% → intrauterine transfusion to raise
haematocrit 40–45%. Preterm delivery may be needed after 34 weeks.
Liley’s zone III (High zone): severely affected fetus and death is imminent. -
Pregnancy > 34 wks → delivery.
Pregnancy < 34 wks → cordocentesis → hct < 30% → intrauterine transfusion
to raise hct 40–45%.
Preterm delivery may be needed after 34 weeks
Treatment of Rh isoimmunisation
Unimmunized mothers: follow an expectant attitude till term. Avoid tendency to overrun the EDD
Immunized mothers: With evidence of hemolytic process in fetus in utero, transfer pt to specialized hosp
Arrange for NICU, exchange transfusion and an expert neonatologist, to attend to affected babies.
Deliver all immunized mothers with evidences of fetal hemolysis in utero
Methods of delivery in rh isooimmunisation
IOL
Amniotomy (low ROMs) is quite effective, if termination is done near
term.
If cervix is ripe, vaginal prostaglandin gel (PGE2) can be used.
Care during Vaginal delivery
Careful fetal monitoring for early detection, of evidence of distress;
Avoid prophylactic oxytocin during 2
nd stage
Gentle handling of the uterus in 3rd stage;
Postpartum hemorrhage prophylaxis
Cesarean section
If premature termination is to be done (say 34–37 weeks), with unfavorable cervix, severe affection plus
urgency of termination, cesarean section is more safer but avoid; Spillage of blood into the peritoneal cavity
and Routine manual removal of placenta.
Rh anti-D IgG given IM to the mother within 72 hours or preferably earlier following child birth provided
the baby born is Rh-positive and direct Coombs’ test is negative.
Also routinely given to nonsensitized patient at 28-32 wks, then 72 hours after birth or any potentially sensitizing
event e.g., ECV, abortion, APH
Anti D is given to all nonsensitized pregnant ladies at expected time of fetomaternal haemorrhage
Mode of action is Ab mediated immune suppression (AMIS), possibly are:
Blocks the Rh-antigen of the fetal cells;
ii) Intact Ab coated fetal red cells are removed from maternal circulation by the spleen
or lymph nodes;
iii) Central inhibition- fetal red cells, coated with anti D Abs interfere the production of
IgG from the B cells.
Dose: 500 IU at 28 and 32 weeks gestation and 250 IU after abortion before 20 weeks pregnancy.
500 IU anti-D within 72 hrs after delivery.
In massive fetomaternal haemorrhage, Kleihauer test is done and dose of anti D calculated accordingly
Calculation of the dose“Kleihauer-Betke test”
If there are 80 fetal erythrocytes in 50 low power fields in maternal peripheral blood films, it represents a
transplacental hemorrhage to the extent of 4 mL of fetal blood.
If the volume of fetomaternal haemorrhage is greater than 30 mL whole blood, the dose of Rh-immune
globulin calculated is 10 µg for every 1 mL of fetal whole blood
Care for newborn in rh isoimmunisation
Early umbilical cord clamping: to minimize any amount of Ab to cross to fetus from the mother.
Keep cord long (15–20 cm):
To allow introduction of umbilical catheter
Exchange transfusion if needed
Collect about 5 mL cord blood from placental end of cut cord for investigation.
a. Clotted blood-ABO and Rh grouping, direct Coombs’ test and serum bilirubin
b. Oxalated blood- Hb estimation and blood smear for presence of immature RBC
Avoid squeezing cord to prevent contamination with Wharton’s jelly. of blood
pregnancy termination in rh isoimmunisation
consider to terminate the pregnancy if there is:
(i) Previous H/O stillbirth with father being homozygous;
(ii) Sudden rise in maternal Ab titre; Optical density difference at 450 nm wave length as plotted on Liley’s chart;
Doppler and ultrasound features of fetal affection.
In mild affection- pregnancy may be continued upto 38 weeks and
then terminate
In severe affection: terminate pregnancy around 34 weeks after
giving maternal steroid.
In premature termination, before 34 weeks, confirm fetal lung
maturation by measuring the L: S ratio in liqour.
In a specialized center, with severe affection before 34 weeks,
intrauterine fetal transfusion (intraperitoneal or intravascular) is done
to continue pregnancy beyond 34 weeks
