A new study has confirmed that non-invasive prenatal testing is more effective than current screening methods at detecting common chromosomal abnormalities (aneuploidies) among low-risk pregnant women.
This study compared the results of NIPT for fetal autosomal aneuploidy with conventional screening for trisomy 21 (Down's syndrome) and trisomy 18 (Edwards' syndrome), which is serum screening for biomarkers with or without ultrasonography and the measurement of fetal nuchal translucency. The study involved more than 1900 women with an average age of 29.6 years and varied ethnic backgrounds, recruited from 21 different antenatal centres.
NIPT correctly predicted all cases of aneuploidy (five cases of trisomy 21, two cases of trisomy 18 and one of trisomy 13 or Patau’s syndrome). Overall, it produced much lower rates of false positive results than screening (0.5% compared with 4.2% for standard screening) and showed much higher predictive ability than screening, with positive predictive values of 45.5% compared with 4.2% for trisomy 21, and 40.0% compared with 8.3% for trisomy 18).
The authors concluded that the performance of NIPT for aneuploidy in a general obstetric population was equivalent to that previously observed among high-risk pregnant women, ie. significantly superior to current screening approaches, saying that ‘cfDNA testing merits serious consideration as a primary screening method for fetal autosomal aneuploidy’. They also estimated that if NIPT had been the sole form of screening provided, the number of invasive diagnostic procedures to confirm suspected aneuploidy would have decreased by 89%, assuming that all women opted for diagnostic confirmation.
These results provide welcome confirmation that the performance of NIPT is high among low-risk as well as high-risk pregnant populations and its use not only improves detection rates but also reduces the number of false positive results. Since invasive testing to confirm positive screening results in a risk of miscarriage of around 1%, the use of NIPT can effectively reduce the numbers of healthy fetuses lost due to invasive testing, as well as reducing the number of women who have to decide whether or not to have such testing. In the UK, where NIPT is currently available commercially but not within the National Health Service (NHS), the current RAPID study is evaluating the suitability of NIPT for Down’s syndrome screening in the NHS.
The test used for the NEJM study was Illumina’s Verifi™; the company recently announced that they intend to seek FDA approval for Verifi as a diagnostic (as opposed to screening) test. Meanwhile, other commercial NIPT providers have begun expansion of their tests to include some of the most common microdeletion syndromes as well as aneuploidies (Natera’s Panorama™ and Sequenom’s MaterniT21™ PLUS. The future looks bright for improved prenatal testing – although it is worth bearing in mind that whilst invasive testing is set to decrease sharply, there will be an ongoing need for it for the investigation of possible fetal chromosomal abnormalities that are much rarer.