Study backs NIPT for Down's syndrome screening pathway

6 July 2016

Non-invasive prenatal testing (NIPT) can form an effective element in a publicly funded national Down’s syndrome screening pathway, according to a UK based study.

NIPT is currently only available in the UK privately or in a research context; it is not part of normal antenatal testing processes. The technique involves taking a sample of the mother’s blood, which contains tiny fragments of DNA from the developing foetus that can be analysed for abnormalities. The non-invasive procedure can be performed earlier in pregnancy than invasive forms of testing such as amniocentesis, and without risk of procedure-related miscarriages. The test is typically highly accurate.

Published in the medical journal BMJ, new results from the NIHR-funded RAPID  (Reliable Accurate Prenatal non-Invasive Diagnosis) research programme report on work with pregnant women attending eight NHS maternity units with differing test provision. NIPT was prospectively offered to 3175 pregnant women with a Down’s syndrome risk (based on standard screening results) of at least 1 in 1000.

The research team found that if NIPT is offered as a contingent test at a risk threshold of 1 in 150 or higher, it can improve the performance of the existing Down’s syndrome screening programme without significantly increasing costs. 

Currently, a pregnant woman with a chance of having a baby with Down’s syndrome is greater than 1 in 150 based on screening results is offered diagnostic testing via amniocentesis, an invasive procedure with a 1% associated risk of pregnancy loss. Introducing NIPT as a contingent test in the UK screening pathway could reportedly reduce the number of these invasive tests carried out, reducing the associated number of miscarriages. For illustration, for 700,000 pregnancies a year, introduction of NIPT would be expected to detect 195 additional cases of Down’s syndrome with nearly 3400 fewer invasive tests and 17 fewer procedure-related miscarriages.Confirming previous research, the study found NIPT to be a highly accurate screening test for Down’s syndrome, but noted that it is important for positive NIPT results to be followed with invasive testing for diagnostic confirmation, as a small number of false positive results can occur.

Uptake of NIPT by women in the study was generally high, though the authors noted that some women chose this option seeking information only and did not necessarily subsequently opt for invasive testing, nor did all women with affected pregnancies opt for termination of pregnancy.  They recommend that maternity services must have coordinated pathway for such families, and note that the overall Down’s syndrome live birth rate may not change significantly following any introduction of NIPT.

Earlier this year the data from the study  was presented to the UK National Screening Committee , as part of its evidence review on NHS implementation of NIPT. The committee recommended to the government that NIPT should be implemented, and the matter is now awaiting a ministerial decision. 

PHG Foundation published the first report  to examine the potential health service implications of NIPT as long ago as 2009, and have been an ongoing contributor to the NIHR RAPID programme.