Rh and other blood group alloimmunizations

Rh and other blood groupalloimmunizationsDr. Agus Rusdhy Hariawan Hamid, SpOG

Flow cytometry can detect fetal red cell and red cell precursors in the maternal circulation in virtually all pregnancies.In some patients, this exposure to fetal red cell antigens produces an antibody response that can be harmful to future offspring. The process is known as red cell alloimmunization (formerly isoimmunization).

Prevention of maternal alloimmunization is almost uniformly successful in the case of exposure to the RhD or Rhesus antigen. Prophylactic immunoglobulin (Rhesus immunoglobulin ; RhIg) is available. RhIg is not effective once the patient has developed endogenous antibodies. Immunoglobulins to prevent sensitization to other red cell antigens are not available.

All pregnant patients should undergo an antibody screen to red cell antigens at the first prenatal visit. In the case of a negative screen in the RhD-negative patient, further testing is unnecessary until 28 weeks gestation. Unless the patients partner is documented to be RhD negative, a 300-g dose of RhIg should be administered.

At delivery, a cord blood sample should be tested for neonatal RhD typing. If the neonate is determined to be RhD positive, a second dose of 300 g RhIg should be administered to the mother within 72 hours of delivery.

In recent years, techniques for fetal surveillance in cases of RhD alloimmunization have evolved to a more noninvasive approach.In the first affected pregnancy, the maternal antibody titer continues to be used as the first level of surveillance.Once the maternal antibody screen indicates the presence of an anti-D antibody, a titer should be ordered.

Ultrasound has revolutionized the surveillance of the anemic fetus. In the past, ultrasound was used to detect fetal hydrops. Unfortunately, this represents an end-stage phase of HDFN with more than twothirds reduction in the fetal hemoglobin below the norm.The most significant breakthrough in the surveillance of the potentially anemic fetus has been the validation of the peak systolic middle cerebral artery (MCA) Doppler velocity.

First sensitized pregnancyFollow maternal titers every 4 weeks up to 20 weeks gestation; repeat every 2 weeks thereafter.Once a critical value (usually 32) is reached in cases of a heterozygous paternal phenotype, perform amniocentesis at 1517 weeks to determine the fetal RhD status. If an RhD-negative fetus is found, no further testing is warranted.If a homozygous paternal phenotype or RhD-positive fetus by DNA analysis, begin serial MCA Dopplers as early as 24 weeks gestation. Repeat weekly 3 times and assess trend. If not rising rapidly, consider MCAs every 2 weeks.If the MCA Doppler is >1.5 MoM, perform cordocentesis with blood readied for intrauterine transfusion (IUT) for a fetal hematocrit of