What test do I need to order based on the results of a Blood Group and Antibody result?
Based on the results of the mother’s blood group and antibody screen, RhD negative women with no anti-D antibodies should be offered RHD NIPT. This includes women with a singleton or multiple pregnancy as the RHD NIPT will identify if at least one of the fetuses is RhD positive and RhD Ig prophylaxis will be recommended if there is a positive result.
Where there is a weak or discrepant D, or clinically significant antibodies (D, C, c, E, K, k, Fy) identified, further testing is recommended (see options below for more information).
RhD positive
Women who are RhD positive do not require the RHD NIPT test.
A repeat antibody screen should be completed between 26-28 weeks gestation.
Ensure the RhD positive status is document in the antenatal/woman’s healthcare record.
RhD negative with no preformed anti-D antibodies
All RhD negative women with no preformed antibodies should be offered the RHD NIPT test between 12-26 weeks gestation.
Women may be offered RHD NIPT up to 32 weeks depending on your organisational policy, as this would prevent the need to administer RhD Ig at 34 weeks and for sensitising events where the fetus is predicted to be RhD negative.
RhD Ig prophylaxis is recommended at 28 weeks if the women presents after 26 weeks and the RHD NIPT has not yet been requested and will not be available prior to 28 weeks gestation.
It is recommended that RHD NIPT is not completed before 12 weeks gestation as there is an increased risk of a false-negative result because of insufficient fetal DNA (some pathology providers may offer testing from 11 weeks where this has been validated)
Women should be provided with the information necessary to determine the risks and benefits of the test and enable them to make an informed decision. Download consumer brochure for RHD NIPT
Consent is assumed following information provision and the woman agreeing to have the RHD NIPT test.
Clinically significant antibodies (D, C, c, E, K, k or Fy) or history of Haemolytic Disease of the Fetus or Newborn (HDFN)
Women with identified clinically significant red cell antibodies should have NIPA testing completed by Lifeblood’s Red Cell Reference Lab , Queensland.
Fetus negative for corresponding antigen – repeat antibody screen between 26-28 weeks gestation.
Fetus positive for corresponding antigen – refer to fetomaternal specialist for further consultation and/or treatment. The woman and fetus will require close monitoring throughout the pregnancy.
RhD negative women with no anti-D antibodies should still be recommended RHD NIPT in addition to further testing for clinically significant antibodies as they may still require RhD Ig therapy.
Where further information is required, in the first instance contact your pathology provider for further guidance.
Weak or Partial D
Women with a weak or partial D blood group may require further molecular testing to determine whether they require RhD Ig.
Where there is a known weak D type 1, 2, 3, the woman should be treated as RhD positive. The woman does not require RhD Ig therapy.
If the woman has a weak D type other than type 1,2,3, the weak D type is unknown or a partial D blood group is detected, the woman should be offered Rhd Ig prophylaxis at 28, 34 weeks and for all sensitising events as if she was RhD negative. The case can be discussed with the testing laboratory pathologist to determine whether their RHD NIPT will be able to determine the fetal RhD type in the setting of the maternal RhD variant. See information for RHD NIPT.
A repeat antibody screen should be repeated between 26-28 weeks gestation.
Where further information is required, in the first instance contact your pathology provider for further guidance.
Result
A report should be available within 10 days from specimen collection. If the result has not yet become available or is required urgently, please contact your pathology provider directly.
The report will have one of four possible results;
Not Reported
Where the specimen does not meet the minimum requirements, the specimen should not be processed and the requesting pathology service or clinical care provider should be notified.
A specimen may be rejected for the following reasons;
• minimum identification requirements are not met or are incorrect
• specimen has been opened prior to processing
• specimen haemolysed
• incorrect tube or form
• gestation < 12 weeks or > 32 weeks gestation
If time permits, a repeat RHD NIPT may be offered, or RhD Ig prophylaxis should be recommended.
A cord blood test should be completed at the birth of the baby to confirm the baby’s ABO and RhD blood group.
If the baby’s RhD blood group is confirmed to be RhD positive, RhD ig is recommended.
Inconclusive
If a specimen returns an inconclusive result, the specimen should be run through the analyser again. If the second result is also inconclusive this should be the final result reported.
This may occur if the quality or amount of the specimen sample is inadequate, or the maternal blood group is a weak D or partial D.
Where the result is inconclusive, RhD Ig prophylaxis should be recommended and a cord blood test completed at the birth of the baby to confirm the baby’s ABO and RhD blood group.
Fetus RhD Positive
Where the fetus is predicted to be RhD positive, the woman should be recommended RhD Ig prophylaxis at 28, 34 weeks and for all sensitising events
A cord blood test should be performed at the birth of the baby to confirm the RHD NIPT results.
Fetus RhD negative
Where the fetus is predicted to be RhD negative, RhD Ig prophylaxis is not recommended.
A cord blood test should be performed at the birth of the baby to confirm the RHD NIPT results.
At the birth of the baby
Cord Blood Specimen
All women should have a cord blood specimen collected following the birth of the baby and this should be collected prior to administration of RhD Ig if required. The cord blood test should be collected on women who have had the RHD NIPT test regardless of the result, to confirm the baby’s blood group and ensure that false-positive and false-negative results are identified and reported.
Where there is a discrepant cord blood result, a capillary blood specimen must be collected from the baby to confirm the baby’s blood group.
RHD NIPT false-positive result.
A false-positive is where the fetus is predicted to be RhD positive and the cord blood confirms the baby to be RhD negative. This result would mean that the woman has been administered RhD Ig unnecessarily during the antenatal period. There is no harm likely for the woman or the baby, and this is the recommended standard of care for all RhD negative women if RHD NIPT is unavailable, has not been attended, declined or the fetal RhD blood group is unknown.
This should be reported in the local hemovigilance/quality and safety system, as well notifying the pathology provider.
RHD NIPT false-negative result.
A false-negative result is where a fetus is predicted to be RhD negative and the cord blood test confirms the baby to be RhD positive. The woman should be offered RhD Ig prophylaxis within 72 hours of the birth to reduce the risk of development of anti-D antibodies. This should be reported in the local haemovigilance/quality and safety reporting system and the pathology provider should be notified immediately.
This must be documented in the woman’s healthcare record.
If the baby’s cord blood RhD group is RhD positive and discrepant with a negative RHD NIPT the mother should be offered RhD Ig postnatally and counselled on her risk of HDFN in future pregnancies.
What is a sensitising event?
If you are RhD negative and your baby is RhD positive, small numbers of the baby’s red cells can cross the placenta into your blood and cause an immune reaction. This is known as sensitisation.
This occurs more commonly during the 3rd trimester of pregnancy and at the birth of your baby.
There are additional events that may cause higher numbers of the baby’s red cells to cross into the mother’s blood. This is known as a sensitising event, and may be caused by;
- during some tests you may have during your pregnancy (such as chorionic villus sampling (CVS) or amniocentesis)
- after miscarriage or termination
- obstetric haemorrhage (heavy, frequent bleeding during pregnancy)
- after an injury or accident to your abdomen
- if your baby is in a breech position and you have an external cephalic version (where doctors turn the baby around inside the womb)
- during labour
- from an ectopic or molar pregnancy