Chapter 11: Rho(D) Isoimmunization

Question 1

For Rh(D) Isoimmunization to occur

Answer 1

• the fetus must have Rh(D)-positive erythrocytes and the mother must have RH(D0-negative erythrocytes
• a sufficient number of fetal erythrocytes must gain access to the maternal circulation; amount can be as little as 0.1 mL
• the mother must have the immunogenic capacity to produce antibodies directed against the D antigen

Question 2

Isoimmuniation

Answer 2

the development of maternal antibodies, which destroy the fetus Rh(D)-positive blood

Question 3

Rho(D) Immune Globulin (RhoGAM)

Answer 3

coats and destroys fetal cells in the maternal circulation

• must be given within 72 hours, and last for 3 months
• to ensure correct amount is given, a fetal screen or Kleihauer-Betke blood test is performed on the woman’s blood after it has been determined that the baby is Rh(D) positive; this test estimates the number of fetal RBCs in the mothers circulation

Question 4

Understanding Rh Factor

Answer 4

anti-Rh antibodies do not spontaneously occur and are only formed if there is sensitization by Rh(D)-positive cells entering the circulation of the Rh(D)-negative person. The Rh(D) negative person develops antibodies against the Rh(D) positive cells; this is why the first pregnancy is not affected, unless mother was previously sensitized during a miscarriage, amniocentesis, or antepartum hemorrhage
-in other pregnancies, if Rh(D)-positive fetuses appear, the fetus may be affected unless the woman receives Rho(D) immune globulin to prevent antibody formation
>Rho(D) immune globulin must be given after birth of EVERY Rh(D)-positive infant

Question 5

What happens if antibodies to the Rh factor are present in the patients blood (i.e. woman is sensitized)

Answer 5

they freely cross the placenta and destroy the RBCs of the Rh(D)-positive fetus
-overtime, the fetus develops an RBC deficiency, the fetal bilirubin levels rise (“icterus gravis”) because of hemolysis of RBCs, and severe neurological disease (“Bilirubin encephalopathy”) may result
>this pathological process triggers a rapid production of erythroblasts (immature RBCs) that are unable to carry oxygen; Erythroblastosis fetalis; fetal anemia and generalized edema (“hydrops fetalis”) develop and lead to fetal congestive heart failure

Question 6

What happens during the prenatal period?

Answer 6

all Rh(D)-negative women receive an antibody titer (indirect Coombs’ test) to determine whether they are sensitized from a previous exposure to Rh(D)-positive blood
>if the test is negative, another antibody titer is obtained at 28 weeks of gestation to rule out sensitization that may have occurred later in pregnancy
-If the woman remains unsensitized, Rho(D) immune globulin is given as a preventative measure to prevent formation of active antibodies during the remainder of pregnancy
-After birth, if the infant is Rh(D)-positive, another dose of Rho(D) immune globulin is given; if the infant is negative, no immune globulin is necessary
-If the prenatal patients indirect Coombs’ test is positive, sensitization has occurred and antibodies against Rh(D)-positive erythrocytes are present in the maternal circulation; in this situation, the patients antibody titer is repeated frequently throughout pregnancy to identify rising level; a rise in the maternal antibody titer is indicative of ongoing antibody formation and an increased likelihood of fetal erythrocyte destruction
>when sensitization has occurred, an amniocentesis may be performed periodically to assess change in the optical density of amniotic fluid; this reflects the amount of bilirubin (bile pigment that remains after RBC destruction) in amniotic fluid
-fluid optical density remains low, it can indicate:
1. that the fetus is Rh(D)-negative (and is in no jeopardy)
2. the fetus is Rh(D)-positive and in no jeopardy
-if fluid remains high: the fetus is experiencing RBC destruction and is in jeopardy

Question 7

Administer and document RhoGAM when clinically indicated

Answer 7

• if the mother is Rh negative and unsensitized and the baby is Rh positive, always check to be sure the patient has received Rho(D) immune globulin (RhoGAM) if indicated before discharge; make sure received appropriate dose
• patients who have miscarried must also be treated
• in cases in which it is not possible to determine the fetus or baby’s blood type, RhoGAM is still given

Question 8

Management

Answer 8

prevention of isoimmunization (a rising anti-Rh antibody titer in an Rh(D)-negative woman) is the goal

• all pregnancy women should be tested for ABO and Rho(D) type along with an antibody screen during first prenatal visit; these determinations made at each pregnancy
• RhoGAM should also be given at any time during the pregnancy when a possibility exists that a patient may be exposed to fetal blood (e.g. CVS, amniocentesis, miscarriage, vaginal bleeding, abortion, and ectopic pregnancy)

Question 9

Safe administration of Rho(D) immune globulin (RhoGAM)

Answer 9

in an Rh(D)-negative woman who is non-sensitized, RhoGAM should be given:
-after delivery of an Rh(D)-positive infant. standard dose is 300 mcg and given within 72 hours of delivery
-educate why she is receiving RhoGAM
-give documentation that she received RhoGAM
>NEVER give RhoGAM to:
-a Rh(D)-positive woman
-A sensitized Rh(D)-negative woman
-an Rh(D)-negative woman who has given birth to a Rh(D)-negative baby
-the baby or father of the baby!

Question 10

Summarizing Care for the Sensitized Rho(D)-Negative Patient

Answer 10

patients with a anti-D antibody titer of greater than 1:4 should be considered Rh sensitized and their pregnancies managed accordingly
-management includes: serial ultrasounds, serial amniocenteses to analyze bilirubin levels in amniotic fluid, percutaneous umbilical blood sampling (PUBS) to obtain fetal hematocrit, and intrauterine blood transfusions for a fetal hematocrit less than 30%
>a delayed manifestation of Rh isoimmunization is neonatal kernicterus, a condition characterized by CNS damage after exposure of the infants brain to hyperbilirubinemia

Question 11

Direct Coombs’ Test

Answer 11

identifies the presence of maternal antibodies in the neonates blood and hemolysis or lysis of RBCs
-positive test must be reported to pediatrician
(checks neonates blood)

Question 12

Indirect Coombs’ Test

Answer 12

detects antibodies against RBCs in the maternal serum

checks moms blood