A Scientific Impact Paper published in BJOG on 11 October reviews non-invasive prenatal diagnosis (NIPD): testing the cell-free DNA that the placenta sheds into maternal blood for a single-gene condition, rather than for the common aneuploidies that standard non-invasive prenatal screening looks for.
The central distinction is between diagnosis and screening. When a family's pathogenic variant is already known, a targeted cell-free DNA test for that variant is treated as diagnostic and does not need invasive confirmation. When the test is used without a known familial variant, for example after an ultrasound finding, it behaves more like a screen. The two share an acronym family but use different laboratory approaches and answer different questions.
The practical gain is timing and safety. A maternal blood sample can be taken from about 8 weeks, earlier than chorionic villus sampling, and avoids the procedure-related miscarriage risk of invasive testing, which the paper puts at around 1 in 200. In the UK the NHS offers NIPD only in limited scenarios, such as a previous affected child or specific ultrasound findings.
For counselling, the useful question is: is there a known variant in this family? If yes, NIPD may answer the question early and without a needle. If not, any cell-free DNA result for a monogenic condition needs to be explained as a probability, not an answer.
- Ask early in pregnancy whether a pathogenic variant is already known in the family — that decides whether non-invasive diagnosis is possible.
- Non-invasive prenatal diagnosis for a known familial variant can be done on maternal blood from about 8 weeks.
- Explain that aneuploidy screening (NIPT) does not test for single-gene conditions such as cystic fibrosis or sickle cell disease.
- Where no familial variant is known, offer invasive testing to confirm any abnormal cell-free DNA result before decisions are made.
- Refer couples with a previous affected child to clinical genetics before or very early in the next pregnancy.
Why it matters
It moves the question for at-risk couples from 'which needle test, and when' to 'is the family variant known'.
Don't overread it
This is an expert review, not a trial; it does not extend diagnostic status to cell-free DNA screens without a known variant.
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