What is the difference between a screening test and a diagnostic test?

A screening test (combined test, NIPT) estimates the chance your baby has a condition — it cannot confirm it. A diagnostic test (CVS or amniocentesis) actually confirms whether the condition is present. A higher-chance screen needs a diagnostic test to know for sure.

No. NIPT analyses fragments of the baby’s DNA in your blood and is a very informative screening test, but a high-chance NIPT result still needs a diagnostic test (CVS or amniocentesis) to confirm.

My screening came back “high-risk” — does my baby have the condition?

Not necessarily. Most people with a higher-chance result go on to have a baby without the condition. It means a diagnostic test can be offered so you can find out for certain if you wish.

Do the diagnostic tests carry a risk to the pregnancy?

CVS and amniocentesis are invasive and carry a small procedure-related risk of miscarriage — the NHS states this as around 1 in 200 (higher in multiple pregnancies). Your own obstetric team can discuss what this means for you, and whether to proceed is a personal decision.

Do I have to have any of these tests?

No. All antenatal genetic testing is optional. You can accept some, all or none, and counselling is available to help you decide what is right for you — there is no single “correct” choice.

Prenatal Genetic Testing in Singapore: Screening vs Diagnostic

Written & reviewed by the BestDoctors.sg editorial team · Last updated 25 Aug 2026 · General information, not medical advice

Prenatal genetic testing is offered during pregnancy to assess the chance of, or to diagnose, certain chromosomal and genetic conditions in the baby. The single most important distinction is that screening tests give a chance or probability and do not diagnose, while diagnostic tests confirm whether a condition is present. A “higher-chance” screening result does not mean the baby has the condition — most people with a higher-chance result have a baby without it — and all prenatal testing is a personal choice, supported by counselling.

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A screening result is a chance, not a diagnosis; a “high-chance” result needs a diagnostic test to confirm. Diagnostic tests carry a small procedure-related miscarriage risk to discuss with your obstetric team. Testing is optional — you may accept some, all or none.

What it is

Prenatal genetic testing covers tests offered during pregnancy to look at the chance of, or to confirm, chromosomal and some genetic conditions. It is offered routinely as part of antenatal care, and uptake is entirely a personal choice. The whole field rests on one distinction: screening estimates a probability without risk to the pregnancy, while diagnostic testing gives a definitive answer but involves a procedure.

Screening tests

Screening tests are non-invasive and carry no procedure risk to the pregnancy. Combined first-trimester screening pairs a nuchal-translucency ultrasound (measuring fluid at the back of the baby’s neck) with a maternal blood test, done around 10 to 14 weeks, and screens for Down’s syndrome (trisomy 21), Edwards’ syndrome (trisomy 18) and Patau’s syndrome (trisomy 13). NIPT (non-invasive prenatal testing) is a maternal blood test analysing fragments of the baby’s DNA in the mother’s blood; it is a more accurate screen, often used after a higher-chance combined result, but it remains a screen — a high-chance NIPT result still needs a diagnostic test to confirm.

Diagnostic tests

Diagnostic tests confirm by examining the baby’s chromosomes, and they are invasive with a small procedure-related miscarriage risk. Chorionic villus sampling (CVS) takes a sample of placental cells, usually between 11 and 14 weeks, and amniocentesis takes a sample of amniotic fluid, usually between 15 and 20 weeks. Both can detect Down’s, Edwards’ and Patau’s syndromes, and diagnostic tests can additionally confirm certain inherited disorders such as thalassaemia, sickle cell disease and cystic fibrosis where indicated.

What conditions are screened

The conditions most prominently screened for are Down syndrome (trisomy 21) and the other trisomies, Edwards’ (18) and Patau’s (13). Diagnostic tests can go further and confirm specific single-gene disorders where there is a known family risk, which is where carrier screening and family history feed into the plan. If you already know that you and your partner carry the same recessive condition, for example, the diagnostic tests can look specifically for it, so it is worth sharing that information with your obstetric team early.

What results mean

A screening result is expressed as a chance — for example “1 in 300” — and classed as higher- or lower-chance. A higher-chance screen does not mean the baby has the condition; it means a diagnostic test can be offered to find out for certain if you wish. A lower-chance screen reduces but does not entirely exclude the possibility, and NIPT, though very informative, is still a screen. Diagnostic tests give a definitive answer for the conditions tested. Understanding this difference in advance helps you decide how much you want to know and which tests, if any, fit your own values — some people want certainty, while others are content with a reassuring screen.

Risks and the personal nature of the choice

Invasive diagnostic tests carry a small procedure-related miscarriage risk: the NHS states amniocentesis risk as about 1 in 200 pregnancies and CVS as less than 1 in 200, both higher in multiple pregnancies — figures to understand as NHS-stated and to discuss with your own obstetric team. A screening result should never be presented as a diagnosis, and testing is entirely a personal choice: a woman may accept some, all or none of it. The framing throughout is respectful and non-directive, and decisions after a diagnosis belong with the woman or couple and their care team. It is also worth knowing that many women choose to have screening for information and reassurance while deciding in advance that they would not want an invasive diagnostic test — and that is a valid choice; each step can be accepted or declined on its own.

Counselling and how to access it

Pre-test and post-test counselling are essential so results are understood and choices are informed and supported, and a genetic counsellor or maternal-fetal-medicine specialist helps interpret results without pressure. In Singapore, antenatal screening, NIPT and, where indicated, CVS and amniocentesis are offered through obstetric services at hospitals such as KKH and NUH, with thalassaemia screening well established. For an obstetric emergency, call 995 or go to the nearest hospital’s delivery service; HealthHub and MOH provide general information. Taking time to ask your obstetric team what each test can and cannot tell you, and weighing the value of information against any procedure risk, is a normal and sensible part of the process rather than a sign of indecision.

Related genetics & genomic-health topics

Sources

NHS — Screening for Down’s, Edwards’ and Patau’s syndromes: nhs.uk
NHS — Amniocentesis: nhs.uk
NHS — Chorionic villus sampling (CVS): nhs.uk

General information only. This guide is general information about a genetics topic and is not a diagnosis, a genetic test result, or personalised medical advice. Genetic test results have implications for you and your blood relatives and should be interpreted with a doctor or genetic counsellor. A raised genetic risk is not a certainty, and a “normal” result does not remove all risk. Do not start, stop or change any medicine or make a medical decision based on a genetic test — including a direct-to-consumer test — without your doctor. Call 995 for any sudden, severe symptoms — such as chest pain, breathlessness or collapse, or a severe drug reaction with a spreading rash, blistering or peeling skin and fever.