Noninvasive prenatal screening for RHD: the Stockholm study

The non-invasive technique to determine fetal RHD status opens the opportunity to change the antenatal screening and Rh-prophylaxis programs. During the period September 2009 to December 2011, we performed a study in the Stockholm area with approximately 27000 pregnancies per year. The study included routine cell free fetal DNA (cffDNA) RHD genotyping in early pregnancy followed by targeted RAADP in gestational week 29 to all RhD negative pregnant women carrying an RHD positive fetus. The new approach in our strategy, compared to previous studies, was that fetal RHD screening was done in early pregnancy at the first antenatal visit and based on a single-exon 4 assay. The implementation of this new screening program in a routine clinical setting is described. The final results of the study are still under analysis. The conclusion until now is that fetal RHD screening in early pregnancy is feasible and accurate with a high sensitivity and specificity, provided samples before gestational week eight were excluded.