Noninvasive prenatal screening for RHD: the 1st national antenatal directed anti‐D prophylaxis program – the Danish model or a guide to robust prediction of need of anti‐D

Abstract

Background As of January 1, 2010, Denmark implemented a national antenatal directed anti‐D prophylaxis program. Prior to this, only postnatal prophylaxis directed by serology of cord blood was practiced. A preparatory work for modernization and optimization of fetal care was carried out by the National Board of Health with participation of leading obstetricians, specialists in fetal medicine, general practitioners, midwives, clinical immunologists and administrators. The promising results of non‐invasive prenatal diagnosis based on cell free fetal DNA enabled an antenatal directed use of anti‐D to those with a D positive fetus, thus eliminating approximately 40% of the antenatal use of anti‐D. The complete program now includes an antenatal RHD screening in gestational week 25, and a postnatal serological RhD typing of cord blood, in both instances followed by administration of anti‐D to those found positive. Aim The explicit aim of the RHD screening was to obtain the highest possible sensitivity to recommend anti‐D in all cases where it might be indicated whereas specificity was of secondary priority. Methods Health services in Denmark are organized in five regions; accordingly screening has been implemented in every region, each using its own in‐house screening methodology. However, all regions have implemented automated DNA purification and the assays are variations over a theme of multiple PCRs covering several exons. A control reaction for DNA purification is obligatory. However, a control for fetal DNA is not included. A working group with members from all regions has implemented a national scheme for quality control. Digital on‐line delivery of results to general practitioners, midwives and obstetricians is implemented in most regions thus cutting down on cost and time. Results The continuation of postnatal serology has allowed a quality control of RHD screening. During the first six months of screening only two false negative results occurred out of 2312 tested (0·087%) suggesting a sensitivity of 99·9%. Due to the sacrifice of specificity some unnecessary use of anti‐D occurred, 39 cases or 1·7%. Discussion The elimination of 38·3% of the use of anti‐D, that is unnecessary and the related clinical contacts balances the expenses for the screening. An unforeseen benefit of the screening has emerged. The availability of the antenatal RHD results at the time of delivery has simplified logistics and preliminary clinical action is taken based on the antenatal result. Only in the very rare occasions of a (false negative) discrepancy between antenatal and postnatal results is communication needed between laboratory, clinician, and patient. The challenge will be to maintain the high standards in a possible future setting without serology serving as a benchmark for quality control.

Integration of noninvasive prenatal prediction of fetal blood group into clinical prenatal care

“…Despite the abovementioned challenges, noninvasive fetal RHD typing is very robust and reliable, also in the first trimester, as a result of a large research endeavor that has generated technical advances and method refinement. Current assay performances are characterized by near 100% accuracies and sensitivities, surpassing a former assessed overall accuracy of 96.5% for detecting plasma cffDNA, based on a meta‐analysis of studies from 1998 to 2005 …”

“…In general, the screening assay must provide a rapid test result at a low cost. Therefore, the setup must be fairly simple with robust sample handling, preferably an automated workflow, and a simple scoring system . Briefly, the current practice is that upon receiving a blood sample, usually from the general practitioner (GP), maternal plasma is separated by standard centrifugation, and DNA is extracted from the plasma.…”

“…Briefly, the current practice is that upon receiving a blood sample, usually from the general practitioner (GP), maternal plasma is separated by standard centrifugation, and DNA is extracted from the plasma. Eluted DNA is then amplified and analyzed, and an interpretation algorithm is used to generate a result (e.g., either RHD positive, RHD negative, or inconclusive) . The recommendation of prenatal prophylaxis must be available before the scheduled time point of prenatal anti‐D injection.…”

“…From 1998 to 2013, several reports have added to the development of the successful clinical application of noninvasive fetal RHD typing, which is now offered in many countries to assist in the management of hemolytic disease of the fetus and newborn (HDFN) . Recently, healthcare systems in Europe have introduced prenatal screening for fetal RHD in all non‐immunized RhD negative women to guide targeted prenatal Rh immunoglobulin prophylaxis . Similar to testing of fetal sex, noninvasive fetal RHD typing may serve as an excellent example of the translational process from development to clinical application of noninvasive DNA testing (NIDT) in prenatal care.…”

Fetal RHD Genotyping from Circulating Cell-Free Fetal DNA in Plasma of Rh Negative Pregnant Women in Iran

“…If the difference between any C t value for RHD exons and GLO gene was \2, this could indicate that the mother has an unexpressed RHD gene and the test result is considered unreliable and further investigation should carried out using the maternal genomic DNA [14]. In cases that fetus is RhD positive, the calculated Ct for RHD gene is at least 4-6 values higher than the Ct for the control gene (GLO) [29].…”