Introduction of a test kit for prenatal molecular genetic determination of the fetal rhesus factor for effective provision of rhesus prophylaxis

During pregnancy and birth an RhD-negative woman carrying an RhD-positive child may develop anti-D antibodies. So-called rhesus prophylaxis is given to all RhD-negative pregnant women in the 28th to 30th week of pregnancy to prevent pregnancy-related alloimmunisation. Allergic reactions or residual risks of transmitting infectious diseases may be side effects. Also, production is costly and in limited quantities only. In Europe, about 40 % of RhD-negative women carry RhD-negative offspring rendering Rh prophylaxis unneccessary in these patients (Clausen et al., 2014).

Fetal RhD status of 17 RhD-negative pregnant women 20 weeks after gestiation was determined in a non-invasive manner using the FastQ® RHD fetal kit of BAG Diagnostics GmbH. Cell-free fetal DNA (cffDNA) was manually isolated from 2 ml of maternal blood plasma. The test was performed according to manufactures instructions. To avoid false negative results due to low cffDNA content, supposedly RhD-negative samples were checked using FastQ® cff control. In addition a positive control (DNA from an RhD positive male) was introduced to detect false positive results. For analysis of the fetal RhD status, exon 5, exon 7 and exon 10 were consulted. To evaluate specificity and reproducibility, results were compared with a partner laboratory.

For 15 of the 17 samples, our results matched those of the partner laboratory after the first run (≙ 88.24 %). Discrepant results were questionable positive results with a relatively weak amplification. As no automated evaluation software is available to date, determination of fetal RhD status is based on subjective assessment of amplification curves. After introducing the positive control and repeating the analyses of the discrepant results, the number of correctly identified samples was increased to 100 %. In addition, the general introduction of the positive control simplifies the identification of false-positive results. No sample was identified as false-negative. Although an automated objective analysis is not yet possible, the results of both labs matched 100 % after the general introduction of a positive control.

The FastQ® RHD fetal kit complemented by the FastQ® cff control kit are reliably suitable for determining the fetal RhD status. Therefore, the test kits can provide assistance in the effective provision of rhesus prophylaxis.

no conflict of interest