Guidance in Laboratory Testing for Prevention, Diagnosis, and Management of HDFN: A Made-in-Canada Approach
Written by:
Gwen Clarke MD FRCPC Haematopathologist, Island Health, Victoria BC and Clinical Professor, Department of Laboratory Medicine and Pathology, University of Alberta
The recognition of maternal anti-D and other antibodies to red cell antigens as the underlying cause of Hemolytic Disease of the Fetus and Newborn (HDFN) marked a significant advancement in maternal-fetal medicine. This knowledge, particularly following the discovery of Rh immune globulin (RhIg) as an effective preventative agent against anti-D development, laid the foundation for a system of laboratory testing during pregnancy.
Laboratory testing is used to assess the risk of HDFN by determining the ABO blood group and screening for the presence of antibodies. This process not only supports prevention—by identifying individuals who are RhD negative and therefore eligible for RhIg—but also aids in the diagnosis and ongoing management of pregnancies in which alloantibodies are detected.
For those who are alloimmunized, laboratory testing enables the careful monitoring of pregnancy through assessment of antibody levels by titration.
Following delivery, testing of cord or neonatal red cells for ABO and Rh blood group, Direct antiglobulin testing and antigen typing in babies born to alloimmunized mothers is also part of the process, helping to predict the risk for jaundice
The timing, technique, and reporting of laboratory testing varies widely across Canada. The Canadian Obstetrical and Paediatric Transfusion Network surveyed hospitals and labs nationwide (survey report: https://www.transfusion.ca/getmedia/62a4f003-6a81-4c9d-b089-420e79bd152a/COPTN-Survey-Report-2019-EN.pdf)), receiving responses from 580 sites. Results showed significant differences in test methods, timing, follow-up procedures, and recommendations.
To address practice variability, a modified Delphi Consensus Conference was organised with ORBCoN. A steering committee reviewed literature and drafted statements, which were then evaluated by a panel of Canadian experts at an in-person conference (https://transfusionontario.org/category/orbcon-resources/presentation-library/perinatal-consensus-conference) . Iterative voting refined the content and wording, resulting in 47 guidance statements on immunohaematology testing for pregnancy and neonatal care, including routine and high-risk scenarios and considerations for neonatal cord blood testing.
(reference: Guidance for Prenatal, Postnatal and Neonatal Immunohaematology Testing in Canada: Consensus Recommendations from a Modified Delphi Process Lieberman, Lani et al. Journal of Obstetrics and Gynaecology Canada , In Press, Available on line 27 August 2025 103088)
Many of the statements correspond to existing practices or necessitate only minimal adjustments for implementation. While certain recommendations involve recommendations for reductions in testing, others entail more substantial changes that may require allocation of additional resources, revised referral strategies, or the development of new tests. Some of the statements which may lead to practice changes are outlined below:
Recommendations for Reduced Testing:
- Statement L2 : A Routine ABO RhD and antibody screen may not be necessary at 28 weeks gestation for either RhD positive or RhD negative pregnancies.
- Statement L4: Maternal ABO, RhD and antibody screen at the time of delivery is only recommended when:
- There is no prior test during the current pregnancy and/or
- There is a clinically significant antibody and/or
- The risk of maternal transfusion is increased and/or
- The risk of neonatal transfusion is increased.
- Statement L7: For any pregnancy less than 12 weeks (0 days) gestational age experiencing an abortion (threatened, spontaneous or therapeutic) an ABO, RhD and antibody screen are not recommended and RhIG is not required.
(reference: VanderMeulen H, Shuman M, Fam PN, Berman R, Callum J, Clarke G, Lieberman L, Walsh C, Thorne J, Yan MTS. Transfusion Testing During Routine Pregnancies: Consensus Recommendations from a Modified Delphi Process. J Obstet Gynaecol Can. 2025 Jul 10;47(9):103034. doi: 10.1016/j.jogc.2025.103034. Epub ahead of print. PMID: 40651573.)
Recommendations for new Testing and Referral:
- Statement H4: For patients with clinically significant antibodies to RhD, C/c, E or K, non invasive prenatal testing (Cell free fetal DNA (cffDNA testing of maternal plasma) is recommended to determine if the fetus is at risk.
- Statement H3: For anti K antibodies early consultation with Maternal Fetal Medicine is recommended.
(reference: N Robitaille N and K Fung Kee Fung et al. National Consensus Statements for Prevention of Maternal Rhesus (RhD) Alloimmunization and Management of Alloimmunized Pregnancies: A Delphi Process JOGC, in press
The statements conform to CSA Z902-25 standards for Blood and Blood Components where relevant standards exist and are also concordant with recent guidance from the Society for Obstetrics and Gynecology of Canada (SOGC) and the Canadian Paediatric Society (CPS).
(references: Guideline No. 448: Prevention of Rh D Alloimmunization.Fung-Kee-Fung, KarenWong, KarenWalsh, JenniferHamel, Candyce Clarke, Gwen et al. Journal of Obstetrics and Gynaecology Canada , Volume 46, Issue 4, 102449 and
Eugene Ng, Gabriel Altit, Chloe Joynt, Nicole Radziminski, Michael Narvey, Fetus and Newborn Committee: Guidelines for detection and management of hyperbilirubinemia in term and late preterm newborns (≥35 weeks gestational age) from: https://cps.ca/en/documents/position/hyperbilirubinemia-newborns)
This guidance is designed to be flexible for various clinical settings across Canada and aims to harmonize practice. While some statements are aspirational and will require new transport logistics, referral processes, and updates to lab information systems others will be quickly achievable. Tools are being developed to support implementation and knowledge translation, facilitating adoption of these Canadian recommendations for improved care.