The Royal College of Obstetricians and Gynaecologists has issued Scientific Impact Paper No. 80 on cell-free fetal DNA testing for single-gene (monogenic) conditions. It is an expert review, not a trial. Single-gene conditions together affect about 1 in 100 births, and fetal DNA from the placenta can be found in the mother's blood from early pregnancy.
The paper's central distinction matters in counselling. Non-invasive prenatal testing (NIPT) screens for common aneuploidies such as trisomy 21. Non-invasive prenatal diagnosis (NIPD) looks for a specific single-gene variant. They use different methods, and when the family variant is already known, NIPD is diagnostic and needs no confirmation by amniocentesis or chorionic villus sampling.
NIPD can be done from about 8 weeks, earlier than invasive testing, and carries none of the roughly 1 in 200 procedure-related miscarriage risk. In the UK's NHS it is currently offered only in limited situations: a previous affected child, or ultrasound findings that point to particular conditions.
In practice the test depends on knowing what to look for, so the family history and parental samples come first. Where NIPD is available in India, and for which conditions, is not set out in this paper and should be checked locally; invasive testing remains the established route where it is not.
- Separate the two in counselling: NIPT screens for aneuploidy, NIPD diagnoses a specific single-gene variant.
- For a couple with a known familial variant, ask early whether NIPD is available, since it can be done from about 8 weeks.
- A known-variant NIPD result is diagnostic and does not need invasive confirmation.
- When a scan suggests a single-gene condition, take a three-generation family history and arrange parental samples promptly.
- Where NIPD is unavailable, invasive testing remains the standard route, with its roughly 1 in 200 miscarriage risk explained.
Why it matters
Confusing NIPD with routine NIPT leads couples to think a low-risk screen has excluded a single-gene condition, which it has not.
Don't overread it
This is an expert review, not new trial evidence, and it describes UK availability; access elsewhere may be quite different.
The statistics, in plain English
The 1 in 200 figure is the commonly quoted procedure-related miscarriage risk for amniocentesis and CVS; it is an approximate average, and many units now quote lower rates. The 1 in 100 births figure covers all single-gene conditions combined, most of which are individually rare.
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