What Causes Isoimmunization?
During her first pregnancy, an rh negative blood of woman may become sensitized to Rh antigens by:
- Being exposed to a positive blood type of rh factor for fetal blood antigens inherited from the father.
- Receiving alien Rh antigens from a blood transfusion, causing agglutinins to develop.
- Receiving inadequate doses of Rho (D) or failing to receive Rho (D) after significant fetal-maternal leakage from abruption placentae.
Subsequent pregnancy with an Rh-positive fetus provokes increasing amounts of maternal agglutinating antibodies to cross the placental barrier, attach to Rh-positive cells in the fetus, and cause hemolysis and anemia. To compensate for this, the fetus steps up the production of RBCs (red blood cells), and erythroblasts (immature RBCs) appear in the fetal circulation. Extensive hemolysis results in the release of large amounts of unconjugated bilirubin, which the liver can’t conjugate and excrete, causing hyperbilirubinemia and hemolytic anemia.
What To Look For?
What Rh-Tests Tell You?At the first pregnancy visit, an anti-D antibody titer should be performed on all women with rh negative blood type origin. If the results are normal (titer is 0) or the titer is minimal (a ratio below 1:8), the test will be repeated at week 28. No therapy is needed at this time.
Sensitive BloodAn anti-D antibody titer of 1:16 or greater indicates rhesus factor sensitization. Continued titer monitoring will occur every 2 weeks for the remainder of the pregnancy. Amniocentesis will be performed approximately every 2 weeks to evaluate the status of the fetus.
During the amniocentesis, the fluid density of the amniotic fluid is determined using spectrophotometry. The results are plotted on a graph and correlated with gestational age to determine the extent of involvement and the amount of bilirubin present.
Also, amniotic fluid analysis may show increased bilirubin levels (including possible hemolysis) and increase anti-Rh titer. Radiologic studies may show edema and, in those with hydrops fetalis (edema of the fetus), the halo sign (edematous, elevated, subcutaneous fat layers).
Treatment of rf-factor incompatibilityTreatment focuses on preventing rh factor in pregnancy by administering RhoGAM to any unsensitized rh negative blood type origin woman as soon as possible after the birth of an rh baby positive or after spontaneous or elective abortion. In addition, screening for Rh Isoimmunization or irregular antibodies is indicated for the following mothers:
- With rh-negative and pregnancy during their first prenatal visit and at 24, 28, 32, and 36 weeks of gestation.
- Rh-positive mothers with a history of transfusion, a neonate with jaundice, stillbirth, cesarean birth, induced abortion, placenta previa, or abruption placentae.
Towering TiterIf the mother’s Rh antibody titer is high, she may be given high doses of gamma globulin to help reduce fetal involvement, hoping to interfere with the rapid destruction of fetal RBCs. The fetus may receive a blood transfusion in utero via an injection of RBCs directly into a vessel in the fetal cord or instillation in the fetal abdomen via amniocentesis. After birth, the neonate may receive an exchange transfusion to removed hemolyzed RBCs and replace them with healthy blood cells.
What To Do?
- Assess all pregnant women for possible blood type compatibility.
- Expect to administer RhoGAM for Rh-negative women after transfusion reaction, ectopic pregnancy, spontaneous and induced abortion, or during the second and third trimesters to women with abruption placentae, placentae previa, or amniocentesis.
- Assist with intrauterine transfusion as indicated; before intrauterine transfusion, obtain a baseline FHR. Afterward, carefully observe the mother for uterine contractions and fluid leakage from the puncture site. Monitor FHR for rapid or slow hear rates.
- Prepare the pregnant woman for a planned delivery, usually 2 to 4 weeks before term date, depending on maternal history, serologic tests, and amniocentesis.
- Assist with labor induction if indicated from the 34th to 38th week of gestation. During labor, monitor the fetus electronically; obtain capillary blood scalp sampling to determine the acid-base balance.
- Provide emotional support to the patient and her family.
- Encourage the patient and her family to express their fears concerning possible complications of treatment.
- Before intrauterine transfusion, explain the procedure and its purpose to them. This is to alleviate their anxiety.
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