The short answer
NIPT can usually be done from about 10 weeks. First-trimester blood screening and the nuchal translucency scan are usually done between 10 and 13 weeks. CVS is available roughly 10 to 13 weeks; amniocentesis generally from 15 weeks. The quad screen is a second-trimester blood test, and the detailed anatomy scan is usually around 18 to 22 weeks. The exact weeks — and which tests you are offered at all — vary by country, clinic and pregnancy.
The whole timeline at a glance
| When | Test | What it does |
|---|---|---|
| Before pregnancy, or at the first appointment | Carrier screening | Checks whether the parents could pass on an inherited condition |
| From about 10 weeks | NIPT (also called cell-free DNA screening) | Estimates the chance of certain chromosome conditions |
| About 10–13 weeks | First-trimester blood screening and the NT scan | Combines blood markers and an ultrasound measurement into an estimated chance |
| About 10–13 weeks | CVS | Takes a sample of placenta — can diagnose certain conditions |
| About 15–22 weeks | Quad screen | Estimates the chance of certain chromosome conditions and of spina bifida |
| From about 15 weeks | Amniocentesis | Takes a sample of the fluid around the baby — can diagnose certain conditions |
| About 18–22 weeks | Detailed anatomy scan | Looks at how the baby’s body is developing |
These are typical windows rather than booking instructions. Dating, twins, earlier results and your local screening programme can all move things.
Before pregnancy, or at the first appointment
Carrier screening tests the parents, not the pregnancy. It looks for conditions such as cystic fibrosis, spinal muscular atrophy and the haemoglobin disorders.
Doing it before pregnancy leaves more time to test a partner and think about the options, but it is still useful once pregnancy has begun.
This is also the moment to dig out any laboratory report belonging to a relative with a genetic condition. “It runs in the family” is very hard to test for. An exact gene change turns a broad search into a quick, focused test.
From about 10 weeks: NIPT
NIPT uses a blood sample from you. Most of the DNA in the tube is your own; a smaller share comes mainly from the placenta. It is a strong screening test for the common chromosome conditions — but it is a screen, not a diagnosis.
Having it too early raises the chance of a “no result”, simply because there may not yet be enough placental DNA in the sample. Laboratories differ on the earliest week they will accept.
About 10 to 13 weeks: the first-trimester window
First-trimester screening may combine blood markers with the nuchal translucency (NT) scan — an ultrasound measurement of fluid at the back of the baby’s neck.
NIPT and the NT scan are not the same test and do not replace each other: one reads DNA, the other looks at the baby. The comparison is here.
CVS is the diagnostic option in this earlier window. It takes a small sample of placenta. Because it is placenta rather than the baby, an unusual result occasionally needs clarifying with an amniocentesis later.
From about 15 weeks: the second-trimester options
The quad screen is a blood test that helps when first-trimester screening or NIPT was not done — and it includes a marker for spina bifida and related conditions, which standard NIPT does not screen for at all.
Amniocentesis usually starts after 15 weeks. It takes a small sample of the fluid around the baby, which contains cells from the pregnancy. What the result can tell you depends entirely on which laboratory test is ordered on that sample.
About 18 to 22 weeks: the anatomy scan
This detailed ultrasound looks at the brain, spine, heart, abdomen, face and limbs.
A low-risk NIPT does not replace it. NIPT looks for certain chromosome differences; the scan can find physical differences that no DNA screen was ever designed to detect.
If something is spotted, it may lead to a more detailed scan, a fetal heart scan, genetic counselling or diagnostic testing. It does not automatically mean a chromosome condition.
Build the plan around decisions, not a checklist
Before agreeing to a test, it is worth asking yourself what you would do with each possible result.
Some people want only information that would change their pregnancy care. Others want as much time to prepare as possible. Some prefer a screening step before deciding about a procedure; others, with a known condition in the family, want a definite answer straight away.
Throughout the whole calendar, one distinction does most of the work: a screen changes an estimated chance, while CVS or amniocentesis can actually diagnose the conditions the laboratory tests for.
Sources and further reading
Common questions
- What is the earliest genetic test in pregnancy?
- Carrier screening can be done before you are even pregnant. Once pregnant, NIPT is usually the earliest, from about 10 weeks. CVS may also be offered in the first trimester when a definite answer is needed.
- Is the 12-week scan the same as NIPT?
- No. NIPT is a blood test that looks at DNA from the placenta. The scan is an ultrasound that checks how the pregnancy is developing and, in many places, measures the fluid at the back of the baby's neck.
- Is it too late for genetic testing after 20 weeks?
- Not necessarily, but timing narrows the options. Ask promptly, because services and legal time limits differ from place to place.
- Do I have to have all of these tests?
- No. Screening is optional, and the tests answer different questions. What is useful depends on your family history, earlier results, any scan findings, how many weeks pregnant you are, and what you actually want to know.