A study carried out in Finland has provided more evidence of how we can use fetal rhesus group testing in order to offer anti-D prophylaxis only to those rhesus negative women who are carring rhesus positive babies and thus reduce the number of women who need to consider whether they want to have this.
Anti-D has been offered postnatally for about 40 years (and if this area is new to you, you can find a series of blog posts that I have written to explain this issue beginning here) and, for the past few years, some areas have been offering women antenatal anti-D as well, although the use of anti-D in pregnancy is more controversial, because a significant number of the pregnant women who are offered anti-D in pregnancy are carrying rhesus negative babies and are therefore not at risk of becoming sensitised if they come into contact with their baby’s blood.
The current study – which is described more fully below – further shows that the fetal RHD test, which is carried out on blood taken from the pregnant woman, is accurate. In this study, the blood test was performed at 24-26 weeks of pregnancy. Of the 10,814 women who had their blood tested over a period of two years, only one false negative and seven false positive results were reported.
Introduction: The aim of this study was to assess the accuracy of the non-invasive fetal RHD test at 24-26 weeks of gestation as part of the national antenatal screening programme to target routine antenatal anti-D prophylaxis (RAADP) at 28-30 weeks at women carrying an RhD-positive fetus
Material and methods: A prospective cohort study involving all maternity care centres and delivery hospitals in Finland between February 2014 and January 2016. Fetal RHD genotyping using cell-free fetal DNA in maternal plasma was performed with real-time polymerase chain reaction in a centralised setting. The results were systematically compared with the serological newborn RhD typing. The main outcome measure was the accuracy of the fetal RHD assay; the secondary variable was compliance with the newly introduced RAADP programme
Results: Fetal RHD was screened from 10 814 women. For the detection of fetal RHD, sensitivity was 99.99% (95% CI: 99.92-99.99) and specificity 99.81% (95% CI: 99.60-99.92). One false negative and seven false positive results were reported by the delivery hospitals during two years. The negative predictive value of the test was 99.97% (95% CI: 99.81-99.99). At the end of the study period, over 98% of the RhD-negative women participated in the new screening program
Conclusions: The targeted RAAPD program was implemented effectively in the national maternity care programme in Finland. An accurate fetal RHD screening test allows discontinuation of newborn testing without risking the postnatal prophylaxis programme. In the future, the main area to investigate will be the clinical effect of RAADP on subsequent pregnancies.