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Prenatal screening guide · 2026
These are not alternatives competing on accuracy. One estimates risk without touching the pregnancy; the other establishes a diagnosis.
NIPT is a screening test on a maternal blood sample — no procedural risk, but it estimates probability rather than establishing a diagnosis. Chorionic villus sampling (CVS) and amniocentesis are diagnostic: they sample placental tissue or amniotic fluid and analyse fetal chromosomes directly, giving a definitive answer, at the cost of a small procedure-related risk. Modern series place that risk at roughly 0.1–0.2% above background, considerably lower than the 0.5–1% figures still widely quoted. The two are complementary: NIPT decides who needs a diagnostic procedure; the procedure gives the answer.
| NIPT | Screening. Maternal blood from 10 weeks. No procedural risk. |
|---|---|
| CVS | Diagnostic. Placental tissue, usually 10–13 weeks. |
| Amniocentesis | Diagnostic. Amniotic fluid, usually from 15 weeks. |
| Procedure risk | Roughly 0.1–0.2% above background in modern series |
| Diagnostic tests detect | Full karyotype or microarray — far more than NIPT screens for |
| Counselling | Doctor consultation or specialist teleconsultation before and after testing |
A screening test sorts a population into higher and lower probability groups. It is designed to be safe and widely applicable, and it accepts some false positives and negatives in exchange.
A diagnostic test answers the question definitively for an individual. It examines fetal cells directly, so it is not affected by placental mosaicism in the way NIPT is, and it can detect a much wider range of abnormalities.
Framing these as competitors misses the point. In current practice NIPT does the sorting, and diagnostic testing is offered to those it flags — a sequence that has substantially reduced the number of invasive procedures performed while maintaining detection. See the prenatal testing pathway guide.
| What is sampled | NIPT: maternal blood. CVS: placental tissue. Amniocentesis: amniotic fluid. |
|---|---|
| Timing | NIPT from 10 weeks. CVS usually 10–13 weeks. Amniocentesis usually from 15 weeks. |
| Result type | NIPT: probability. CVS and amniocentesis: diagnosis. |
| Range detected | NIPT: selected trisomies, sex chromosomes, sometimes microdeletions. Diagnostic: full karyotype or chromosomal microarray, detecting far more. |
| Procedural risk | NIPT: none. CVS and amniocentesis: roughly 0.1–0.2% above background in modern series. |
| Turnaround | NIPT: typically 1–2 weeks. Diagnostic: rapid results in a few days, full analysis longer. |
NIPT first for most people — blood draw only, from 10 weeks.
Many people are quoted a miscarriage risk of 0.5% to 1% for amniocentesis. Those figures come from older studies performed before routine continuous ultrasound guidance and with different needle techniques.
Contemporary systematic reviews of large modern series put the procedure-related loss rate substantially lower, in the region of 0.1% to 0.2% above the background risk of miscarriage that exists in any pregnancy at that gestation. CVS carries a broadly comparable risk in experienced hands.
This matters because an inflated risk figure leads people to decline a procedure that would have given them a definitive answer, and to make decisions on a screening result instead. Ask your obstetric unit for their figures, since operator experience and volume affect outcomes.
Other considerations: CVS performed before 10 weeks has been associated with limb defects and is not done; CVS can detect confined placental mosaicism, occasionally requiring a follow-up amniocentesis; and amniocentesis before 15 weeks carries higher risk and is avoided.
Low prior risk, wanting information without procedural risk: NIPT is the appropriate first step.
High-risk NIPT result: diagnostic testing before any decision. CVS if gestation allows, otherwise amniocentesis. See the high-risk result guide.
Structural abnormality on ultrasound: diagnostic testing with chromosomal microarray is usually recommended directly, without NIPT first — NIPT does not screen for the many conditions that could explain a structural finding.
Known familial chromosomal rearrangement or single-gene condition: diagnostic testing directly, since NIPT does not cover these. See MedEx genetic testing services.
Persistent NIPT failure: diagnostic testing is a reasonable alternative route — see the fetal fraction guide.
Whichever route, the decision benefits from a conversation before rather than after. Book a specialist teleconsultation.
No. NIPT is a screening test that estimates probability, while amniocentesis and CVS analyse fetal chromosomes directly and give a diagnosis. They serve different purposes rather than competing.
Contemporary systematic reviews of modern series put procedure-related loss at roughly 0.1 to 0.2 percent above background, considerably lower than the 0.5 to 1 percent figures from older studies. Ask your obstetric unit for their own figures.
Largely a question of gestation. CVS is usually performed between 10 and 13 weeks and amniocentesis from around 15 weeks. CVS can occasionally detect confined placental mosaicism requiring a follow-up amniocentesis.
Yes, and this is sometimes the right choice – for example where a structural abnormality is seen on ultrasound, or where there is a known familial chromosomal rearrangement, since NIPT does not screen for those.
Considerably more. A full karyotype or chromosomal microarray detects a much wider range of abnormalities than the selected conditions NIPT screens for.
NIPT typically one to two weeks. Diagnostic testing can give rapid results within a few days for the common trisomies, with full analysis taking longer.
Weighing up a diagnostic procedure? Ask your unit for their own figures.
Medical disclaimer: This article is general health information and does not replace medical advice, diagnosis or treatment. Laboratory reference ranges differ between laboratories and results must be interpreted alongside your symptoms, medicines and medical history. Speak with a qualified clinician before starting, stopping or changing any treatment. Service details, inclusions and prices can change — confirm them with MedEx before booking.
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