Antenatal reference service

<Anti-D, -c, and antibodies within the Kell system are the antibodies most likely to cause significant fetal disease. Therefore pregnant women with these antibodies should be followed up at monthly intervals until 28 weeks of gestation and at two weekly intervals thereafter to term. Read the Red Cell Immunohaematology user guide for details about testing protocols for anti-K. Tests for the quantitation of anti-D and –c, titration of Kell antibodies and the exclusion of other antibodies are performed.

Pregnant women with antibodies, other than anti-D, -c and Kell should be retested (titrated and further antibodies excluded) once in the third trimester, normally at 28 weeks; the results at this time will determine the frequency of follow-up testing required thereafter.

When anti-D, anti-c or anti-K are detected a sample should be sent from the father of the baby for phenotyping.

This service is provided by the International Blood Group Reference Laboratory (IBGRL) and predicts the blood group status of fetuses at risk from haemolytic disease of the fetus and newborn (HDFN).

The test predicts fetal RhD, Rhc, RhC, RhE blood groups from 16 weeks and Kell (K1) from 20 weeks gestation with high accuracy from a sample of maternal blood. The main purpose of the service is to identify women with antigen-positive fetuses who can then be informed and prepared for careful monitoring during their pregnancy.

It will also identify pregnant women who have antigen-negative fetuses and are therefore not at danger from HDFN. If these women are identified then further clinic appointments, follow-up antibody tests and invasive procedures can be avoided.

Please advise your local blood centre if intra-uterine transfusion or delivery of an at risk baby is planned where exchange transfusion is likely.

Selected phenotyped units, less than five days old, for neonatal exchange transfusion are available on request from your blood centre. These should only be requested once the infant has been delivered and an exchange transfusion has been planned, because once irradiated they have a shelf life of only 24 hours.

Please inform the reference laboratory as soon as any woman with alloantibodies other than anti-D or anti-K is admitted for delivery, whether or not a sample has been referred. This will ensure that suitable antigen negative blood will be swiftly available for the mother and the baby.

It is important to determine the RhD type of the neonates of all RhD negative women as soon as possible after delivery. If RhD positive, a Kleihauer test should be performed on a maternal EDTA sample taken after delivery (within 2 hours) so that any large feto-maternal haemorrhage can be detected.

In any case where the Kleihauer test indicates a FMH > 2mL of fetal red cells, or where the test result is equivocal, a sample (the same as used for the Kleihauer test) can be referred to NHSBT for confirmation by flow cytometry.  Advice on how much additional anti-D is recommended for large bleeds will be provided by an RCI Consultant Haematologist. 

To ensure timely testing, please phone your blood centre if you intend to send samples for flow cytometry. 

Please note that for large bleeds >40mL an intravenous (IV) anti-D preparation is recommended in preference to intramuscular injection. 

Suspected cases of HDFN can be investigated by RCI reference laboratories to detect and identify the causative red cell antibody, including immune ABO antibodies. Tests applied include direct antiglobulin test and eluate from the baby’s cells.

Samples are required from mother and newborn, carefully labelled to distinguish between them