Non-invasive foetal RhD genotyping to guide anti-D prophylaxis: an external quality assurance workshop.

Abstract

Alloimmunisation against the D antigen in pregnant RhD-negative women is preventable using anti-D immune prophylaxis1. A combination of antenatal and postnatal anti-D administration has dramatically reduced alloimmunisation of RhD negative women from 16% to 0.3%1,2. Analysis of cell-free foetal DNA (cffDNA) circulating in maternal plasma facilitates non-invasive antenatal testing of the foetal RhD genotype at an early gestational age3,4. Knowledge of the foetal RhD type allows targeted use of antenatal prophylaxis, avoiding unnecessary treatment of RhD-negative women who are carrying a RhD-negative foetus, and are thus at no risk of immunisation5. Routine foetal RhD genotyping using cffDNA has been introduced as a national service in Denmark, the Netherlands, and Finland, with several other countries also offering the service regionally6,7. Some countries are in the process of national implementation, while others await approval from their national health authorities. As a consequence of the high performance of non-invasive foetal RhD genotyping, cord blood typing has been discontinued in Denmark and the Netherlands1,8. Without confirmatory testing of the neonate’s RhD type, non-invasive foetal RhD genotyping can no longer be verified, and quality control of the assay becomes increasingly important. Additionally, many laboratories require annual external testing as part of their quality control programme. Here, we report the results from an external quality assurance workshop, EQA 2016, in which 22 laboratories participated in testing two plasma samples from pregnant RhD-negative women, with the aim of future development of standards for testing for foetal RhD genotype.