NICE DG31: Non-Invasive Prenatal Testing for Chromosomal Abnormalities
What NIPT Is
Non-invasive prenatal testing (NIPT), also called cell-free DNA (cfDNA) screening, analyses fragments of placentally-derived cell-free fetal DNA circulating in maternal plasma. It can be performed from around 10 weeks of gestation using a maternal blood sample only — no fetal risk. NIPT is a screening test, not a diagnostic test: it reports a "low chance" or "higher chance" result, not a definitive diagnosis.
Accuracy
NIPT is substantially more accurate than first-trimester combined screening. Pooled data from large meta-analyses of cfDNA screening (e.g. Gil et al., Ultrasound Obstet Gynecol 2017) report detection rates of approximately 99% for trisomy 21 (Down's syndrome), with a false-positive rate around 0.04% — markedly better than the combined test's detection rate of ~85–90% at a false-positive rate of ~2–3%. Detection rates for trisomy 18 (Edwards' syndrome) and trisomy 13 (Patau's syndrome) are also high (widely cited as high-90s percent) but consistently reported as slightly lower than for trisomy 21, with correspondingly low false-positive rates. Performance is generally poorer in twin pregnancies and can be affected by low fetal fraction, maternal obesity, and very early gestation.
Where NIPT Sits in the Screening Pathway
NIPT is not a first-line universal test in the NHS. The pathway is:
- First-line screening: the combined test (nuchal translucency + maternal serum PAPP-A and beta-hCG) at 11+2 to 14+1 weeks (NG201, recommendation 1.2.14), or the quadruple test in the second trimester for women booking later.
- Higher-chance result (conventionally a chance of 1 in 150 or greater): the woman is offered a choice between (a) proceeding directly to invasive diagnostic testing (CVS or amniocentesis), or (b) NIPT as a contingent second-line screening test to refine the risk estimate before deciding on invasive testing.
- NIPT result: a "low chance" NIPT result does not require further testing (though it does not reduce the chance to zero). A "higher chance" NIPT result must be confirmed with diagnostic testing (CVS or amniocentesis) before any clinical decision is made — NIPT alone is never sufficient grounds for a diagnosis or a decision about the pregnancy.
The clinical value of inserting NIPT as a contingent step is that it markedly reduces the number of women proceeding to invasive testing (and the associated procedure-related miscarriage risk, commonly quoted as roughly 0.5–1%) compared with acting on combined-test results alone, because it filters out the large majority of combined-screening false positives.
High-Yield Exam Points
- NIPT is a screening test, never diagnostic — a higher-chance NIPT result always requires CVS or amniocentesis for confirmation.
- In the NHS pathway, NIPT is a contingent/second-line test offered after a higher-chance combined (or quadruple) test result — it is not first-line universal screening in the UK.
- Detection rate for trisomy 21 is markedly higher (~99%) and the false-positive rate markedly lower (~0.04%) than the first-trimester combined test.
- NIPT reduces unnecessary invasive testing and its associated miscarriage risk by filtering out most combined-screening false positives.
- There is no NICE code "DG31" for NIPT — the real DG31 concerns ovarian cancer testing. NIPT policy is set via NG201 (Antenatal care) and the NHS Fetal Anomaly Screening Programme (FASP), not a dedicated diagnostics guidance.
Source: National Institute for Health and Care Excellence (NICE) — **correction note:** NICE diagnostics guidance code DG31 is *not* about NIPT. DG31 is "Tests in secondary care to identify people at high risk of ovarian cancer" (published 15 November 2017), since reclassified as HealthTech guidance HTG453 — an unrelated topic. NICE has no standalone diagnostics guidance dedicated to NIPT for fetal trisomies. The current UK guidance on this test lives in two places: NICE guideline **NG201** (Antenatal care), which offers screening for Down's, Edwards', and Patau's syndromes and directs women into the **NHS Fetal Anomaly Screening Programme (FASP)**, and the FASP pathway itself (run by the UK National Screening Committee), which sets out the cfDNA/NIPT contingent-testing protocol in detail. This filename is retained as `dg31` for corpus continuity, but no exam question should cite "DG31" as the source for NIPT content. (NG201 published 19 August 2021, last reviewed 27 December 2024)
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