NIPT & detection of foetal aneuploidy and avoiding unnecessary Anti D prophylaxis at antenatal period

  

The policy of offering cffDNA testing to all RhD-negative women at about 16 weeks’ gestation to avoid anti-D administration when the fetus is RhD-negative-seems to be a novel idea, This is an another indication of NIPT.

Recent advances in genomic sequencing and bioinformatics have led to the development of noninvasive detection methods with detection rates approaching those obtained with amniocentesis and chorionic villus sampling (CVS) . Recently, a novel prenatal testing method has become available. This method, known as noninvasive prenatal testing (NIPT), is a molecular approach for assessing fetal aneuploidy using cell-free fetal deoxyribonucleic acid (cffDNA) from the plasma of pregnant women.

 

NIPT has a false positive rate of about 0.2 % and detection rate of about 98 % for Down syndrome .NIPT has been used for assessing abnormalities such as trisomy 21, trisomy 18, and trisomy 13.

Approximately 10–15 % of the cell-free deoxyribonucleic acid (cfDNA) in maternal blood comprises cffDNA .The half-life of cffDNA is short, and it clears from maternal circulation soon after delivery .Hence, there is no risk of fetal DNA persisting from one pregnancy to the next and confounding test results.

For women infected with hepatitis B, hepatitis C, and/or human immunodeficiency virus (HIV), the use of noninvasive methods of prenatal risk assessment is recommended, using tests with high sensitivity and low false-positive rates, such as serum screening combined with nuchal translucency, anatomic ultrasound, and noninvasive molecular prenatal testing .

Among other factors, cost implications for introducing this new technology in clinical practice will need to be considered. Noninvasive fetal Rhesus (Rh) D genotyping, using cell-free fetal DNA (cffDNA) in the maternal blood, allows targeted antenatal anti-RhD prophylaxis in unsensitized RhD-negative pregnant women .

 

 

A prospective, interventional, cross-sectional observational study, to determine whether a policy of offering cffDNA testing to all RhD-negative women at about 16 weeks’ gestation to avoid anti-D administration when the fetus is RhD-negative could be implemented successfully in the NHS without additional funding, was set-up by Soothill et al. The total use of anti-D doses fell by about 29 % which equaled to about 35 % of RhD-negative women not receiving anti-D doses in their pregnancy unnecessarily .The authors strongly recommended that this service be extended to all the UK NHS services.

Reserachers have  recently reviewed the clinical validation and implementation studies of maternal blood cfDNA analysis to define the performance of screening for fetal trisomies 21, 18, and 13 and sex chromosome aneuploidies . The  meta-analysis on the performance of cfDNA Testing in screening for aneuploidies  reported cfDNA results in relation to fetal karyotype from invasive testing or clinical outcome. Screening for trisomy 21 by analysis of cffDNA in maternal blood is superior to all other traditional methods of screening, with higher DR and lower FPR