Foetale resus-D-typering toegevoegd aan prenatale screening op infectieziekten en erytrocytenimmunisatie[Foetal Rhesus-D typing added to antenatal screening for infectious diseases and erythrocyte immunisation]

Objective In the Netherlands, postnatal anti-Rhesus(D)-prophylaxis (anti-D) for RhD-negative pregnant women was introduced in 1969, followed by the introduction of antenatal anti-D administration in 1998. Screening for RhD and administration of anti-D has led to a reduction of the incidence of RhD alloimmunisation from 3.5% in 1969 to 0.29% in 2004. However the efficiency of the antenatal anti-D administration was moderate, as anti-D prophylaxis was unnecessarily given to 40% of the RhD-negative women carrying a RhD-positive child (determined after birth). The discovery of fetal DNA in the blood of pregnant women gave the opportunity for fetal RhD-typing (fRhD), and thus for selective antenatal administration of anti-D to women carrying a RhD-positive child rather than universal administration. From 1 July 2011, fetal RhD-typing was added to the Dutch Antenatal Screening Programme. The objective of this study was to evaluate the accuracy of the new test method and the implementation of the expanded Screening Programme. Design Descriptive, national Method Sanquin laboratory performed fRhD-typing using real-time quantitative PCR, and also performed RhD-typing on cord blood. The results from the first year after implementation were used for this study. The National Institute of Public Health in the Netherlands records all results of the antenatal screening programme coming from laboratories and health care professionals in a national database. Additional data on cord blood testing (occasionally performed by laboratories other than Sanquin) and on the administration of anti-D were obtained from this database. Results of fRhD-typing were compared to results from cord blood RhD typing of the child to determine the accuracy of the newly introduced fRhD test method. In addition, national coverage of the fRhD-typing and anti-D administration were investigated. For a sample of 210 pregnant women with missing results on fRhD-typing and a sample of 50 women with missing postnatal anti-D administration, the health care professionals were contacted to investigate the reason for these lacking data. Results 0.05% of the fRhD results was false negative (9/18,383; 95% CI: 0.02-0.09), and 0.85% was false positive (157/18.383; 95% CI: 0.73-1.00). fRhD was incorrectly omitted in fewer than 1% of pregnant women. In 96.1% of the pregnant women, antenatal administration of anti-D prophylaxis was recorded. Recording of postnatal anti-D administration turned out to be lower (92%), but locally recorded data showed that postnatal anti-D was omitted in fewer than 2% of cases. Conclusion The percentage of false negative fRhD was statistically significantly lower (p < 0.05) than the critical limit of 0.25% determined beforehand by the Programme Committee of the Dutch Antenatal Screening Programme for Infectious Diseases and Erythrocyte Immunisation. The percentage of false positive fRhD was considered acceptable, and implementation of fRhD was more or less complete. Routine RhD-typing on cord blood was therefore omitted from January 2013. Antenatal and postnatal anti-D administration is now specifically indicated for RhD-negative pregnant women when fRhD is positive, thus saving about 10,000 unnecessary antenatal anti-D administrations per year. RhD-typing on cord blood is now performed only if the RhD blood type of the child of a RhD-negative mother is unknown at delivery, if a positive fRhD was found for multiple births, and in exceptional situations, e.g. if fRhD typing is not possible due to a rare genetic variation.