(a) ABO grouping, 2 Rh typings, and 3 tests for unexpected antibodies.
(b) If the woman is Rh-negative, her blood should be routinely checked
for the RhO variant (DU). When using a suitable serum, the result of this test should be
read microscopically if macroscopically negative and the results recorded to indicate a
(2) In Rh-negative women whose results in an original antibody-detection
test were negative, the test should be repeated at approximately 32 weeks. If the
results of this test are negative, no further prenatal serologic tests need be made. All
positive antibody-detection tests require identification of the antibody. Antibodies which
are not formed as a result of known RBC sensitization (for example, anti-Lewis,
anti-lH, anti-H, and anti-I) are relatively common during pregnancy, but do not cross the
placenta. Treatment of the serum with two-mercaptoethanol or dithiothreitol will aid in
distinguishing lgM from lgG antibodies. All significant antibodies should be titered and
scored at least monthly or until amniocentesis is begun. A change in titer of more than
two tubes (over fourfold) or a score change of more than ten is significant. Changes in
titer of one tube or score changes of less than five are not significant. Score changes of
5 to 10 and titer changes of two tubes are equivocal. When prenatal testing reveals an
unexpected antibody, freeze the serum (-30C) for comparison with subsequent
samples from the patient.
(3) The principal value of antibody titration is to identify those women who
are candidates for amniocentesis. A rising titer in the first affected pregnancy indicates
that the baby probably will be affected with HDN. Serial titers in subsequent
pregnancies may have some prognostic value. Antibody titration is generally not helpful
in the prenatal management of ABO hemolytic disease.
(4) In Rh hemolytic disease, Rh phenotyping of the child's father can be
helpful in predicting the outcome of future pregnancies. In other types of HDN, the
father's RBCs can be tested to determine if he is homozygous or heterozygous for the
gene producing the immunizing antigen.
b. Amniotic Fluid Examination.
(1) Examination of the amniotic fluid for bilirubin like pigment is the best
available method for evaluating the degree of hemolysis occurring in the infant and the
infant's general condition. There are two indications for performing amniocentesis:
(a) Antiglobulin titer of 1:32 or higher for an unexpected antibody
known to be capable of causing HDN. (This minimal critical titer may vary slightly in
different laboratories because of differences in technique.)
(b) A history of a previously affected baby with RhO or other HDN,
regardless of the maternal antibody titer.