Prenatal Tests: Screening, NIPT and Diagnostic Options
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Start with three questions: what condition is this test looking for, what does the result mean, and what choices follow? Availability and timing depend on your location and individual care plan.
Screening is not a diagnosis
Screening indicates a higher or lower chance of a specified condition. Diagnostic testing can answer particular clinical questions, but no single test excludes every condition. CVS and amniocentesis are important diagnostic options; specialised non-invasive prenatal diagnosis is also available for certain inherited conditions. Ask what your particular test can establish.
NHS: screening choices and timing · NHS Genomics: non-invasive prenatal diagnosis · NHS screening programme: CVS and amniocentesis
NIPT looks at cell-free DNA
NIPT uses a blood sample containing maternal and placental DNA. It screens for selected chromosome conditions. The conditions included and the test's performance vary. A higher-chance result is not a diagnosis; discuss confirmation with CVS or amniocentesis before decisions based on that result. An inconclusive result also needs a follow-up plan.
Read percentages with the right denominator
These are different questions. A 5% false-positive rate does not mean only 5% of positive results are false. Ask for the chance that your own result represents the condition, and the uncertainty around it.
| Measure | What it describes |
|---|---|
| Detection rate / sensitivity | How often the screen identifies pregnancies that have the condition. |
| False-positive rate | How often a pregnancy without the condition receives a positive screen. |
| Positive predictive value | How often a positive screen corresponds to the condition being present. |
New England Journal of Medicine: false-positive rates and predictive value
A timetable is local, not universal
For example, NHS screening includes the combined test around 11–14 weeks and the anatomy scan around 18–21 weeks. The anatomy scan examines development but cannot find every condition. Gestational-diabetes testing, Group B Strep testing and additional scans follow local protocols and your clinical circumstances.
NHS: screening choices and timing · NHS: 20-week screening scan · NHS: antenatal care
Discuss diagnostic options without pressure
CVS samples placental tissue; amniocentesis samples amniotic fluid. Both can investigate particular genetic conditions and carry a small miscarriage risk. Ask which analysis is planned, its limitations, the individual procedure risks and how long results may take. Screening results, scan findings or family history can lead to this discussion.
Common questions
Does a low-chance NIPT result replace the anatomy scan?
No. NIPT and ultrasound answer different questions. Follow the scan plan agreed with your maternity team.
Do I have a choice about screening?
NHS screening is offered as a choice. Ask your own care team about the purpose, benefits, limitations and timing of each test, and discuss your preferences.
Sources
Checked 3 October 2026. These are editorial summaries of the linked guidance; no clinical review of this page is claimed.