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Prenatal screening choices
First-trimester screening
First-trimester screening is a way of asking how likely some chromosomal conditions are early in pregnancy. It can help with planning, but it does not by itself tell you for certain whether the baby is affected.
The common choices are a non-invasive prenatal test (NIPT) from 10 weeks, a nuchal translucency (NT) scan in the 11 to 14 week window, a combined screening pathway using the scan plus a blood test from your arm, or routine care without first-trimester chromosomal screening. The best choice depends on how much information you want and what you would do with it.
NIPT is a blood test. The NT scan is an ultrasound. Chorionic villus sampling (CVS) and amniocentesis are diagnostic tests used when more certainty is wanted. The anatomy scan still matters later even if early screening looks reassuring.
Main options
What the main early screening tests actually are
Patients often hear the abbreviations before anyone explains them properly. These are the common first-trimester options in plain language, and they are not all doing the same job.
These tests are only useful if the result would genuinely help you decide on a next step. For some people that means reassurance. For others it means deciding whether they would want a more definite test if screening looked higher chance.
Age also matters. As maternal age rises, the chance of some chromosomal conditions rises too, so age is built into the screening algorithms rather than being treated as a separate issue.
One practical drawback of NIPT is cost. It is often more expensive than combined screening and is not always funded routinely. In some pregnancies, if the blood test, the NT scan, or the combined screening result comes back higher chance, a medical aid may then fund NIPT as a next screening step.
A key difference
Screening tests and diagnostic tests are not the same thing
The most important distinction is this: a screening test tells you whether a condition is more likely or less likely. A diagnostic test is used when you want much more certainty.
Screening tests
Used first in most pregnancies
- Estimate whether a condition looks lower chance or higher chance
- Usually involve a blood test, an ultrasound, or both
- Do not put a needle into the pregnancy itself
Diagnostic tests
Used when more certainty matters
- Can give a much more definite answer than screening
- Include chorionic villus sampling (CVS) and amniocentesis
- Carry a small procedure-related risk, including miscarriage
Screening tests do not put a needle into the pregnancy. Diagnostic tests do, which is why they carry a small procedure-related risk, including miscarriage.
What it means in practice
The words sound similar, but they are not the same kind of test
- Screening tests estimate chance: NIPT and combined first-trimester screening are examples. They help decide whether a condition looks lower chance or higher chance.
- Maternal age is part of the calculation: age is used together with the scan and blood results when the algorithms estimate risk.
- Screening can still be useful without being definite: a low-risk result can be reassuring, but it does not exclude every chromosome or structural concern.
- Chorionic villus sampling (CVS) is usually the earlier diagnostic option: it tests placental tissue when more certainty is wanted sooner.
- Amniocentesis is usually the later diagnostic option: it tests amniotic fluid later in pregnancy if more certainty is wanted after the first-trimester window.
- Diagnostic tests do carry risk: because they are invasive, there is a small procedure-related risk, including miscarriage.
- Not everyone with a higher-chance result wants diagnostic testing: the right next step depends on what you want to know and what you would do with the answer.
How it usually flows
How screening usually leads to next steps
In most pregnancies we start with screening because it is safer and often gives enough information for planning. Diagnostic tests are then discussed when screening looks higher chance, comes back unclear, or when more certainty would genuinely change what happens next.
Step 1
Choose one screening route first
Most patients start with NIPT, the NT scan with bloods, or routine care without first-trimester chromosomal screening. We do not usually stack every screening test together at the same time.
Step 2
If the result is lower chance, routine care usually continues
A lower-chance result may provide reassurance, but it is not a guarantee. Pregnancy care still continues, and the anatomy scan later in pregnancy still matters.
Step 3
If the result is higher chance, pause and clarify the next screening step
That may mean proper counselling first, repeat bloods in some situations, or discussing NIPT if a blood test or NT-based pathway came back higher chance. In some pregnancies, a medical aid may then fund NIPT as the next screening step.
Step 4
Diagnostic tests are for when more certainty is worth the risk
If more certainty would change planning or decisions, chorionic villus sampling (CVS) or amniocentesis may be discussed. These invasive diagnostic tests are arranged with an independent subspecialist outside my practice.
Important
We do not usually go straight to chorionic villus sampling or amniocentesis
Because NIPT is highly accurate for the common trisomies, it has in many pregnancies reduced the need to go straight to invasive testing as a first step. In practice, it has often taken that place. But it is still a screening test, not a diagnostic one.
CVS and amniocentesis remain important when a result is higher chance, unclear, or when you want a more definite answer. They are more invasive and do carry a small procedure-related risk, which is why they are usually reserved for pregnancies where that extra certainty would genuinely change what happens next.
Timing at a glance
When each option becomes useful
The timing is part of the test. A very good test still loses value if it is done outside the useful window, or without a clear plan for what happens if the answer is unexpected.
From 10 weeks
The NIPT blood test becomes possible
If you want blood-based screening for the common trisomies, this is usually when it becomes available.
11 to 14 weeks
The NT scan and combined screening window
This is the usual window for the nuchal translucency scan and for combined first-trimester screening pathways that depend on scan timing.
10 to 13 weeks
CVS can be the earlier diagnostic option
If you want diagnostic testing earlier in pregnancy, chorionic villus sampling (CVS) is usually the earlier option. It tests placental tissue and is used when more certainty is wanted.
Around 15 to 16 weeks
Amniocentesis is the later diagnostic option
If diagnostic testing is chosen later, amniocentesis is usually the next option. It uses amniotic fluid rather than placental tissue and is typically done later than CVS.
In a combined screening pathway, the blood sample is taken from your arm. It does not put the pregnancy at risk by itself; the risk discussion mainly applies to diagnostic tests such as CVS or amniocentesis.
If you are already past 14 weeks, it does not mean all useful information has been lost. The NT window may be gone, but depending on gestation NIPT may still be discussed, and amniocentesis is the later diagnostic option if more certainty is wanted.
The anatomy scan at 18 to 22 weeks still matters later, even after low-risk first-trimester screening.
Focused NT and anatomy scans are often performed by providers with additional dedicated fetal-scanning training and high case volume. That is about the purpose of the scan, not because routine pregnancy scanning in the rooms was “the wrong scan”.
Using the information
What do people actually do with these results?
The most important thing is not to treat a screening result as a diagnosis before it has even been explained properly. The next step depends on what the result shows and what matters most to you.
Some patients continue pregnancy with clearer planning
A low-risk result may provide reassurance, even though it is never a guarantee. If a condition is confirmed or strongly suspected, some patients continue the pregnancy but use the information to plan better: more focused scanning, specialist review, delivery planning, and neonatal care where needed.
Some patients want more certainty first
If screening comes back higher chance, or if there is no result, some patients want a more definite answer before making further plans. That is when specialist review, repeat bloods, CVS, or amniocentesis may be discussed depending on the timing.
Some patients want to discuss whether to continue the pregnancy
For some serious conditions, the information may also lead to a conversation about whether continuing the pregnancy is right for you. Some patients want to continue and prepare. Others want to discuss termination. The role of counselling is to explain the information clearly and support informed choices, not to push you in one direction.
If NIPT comes back with no result, that is its own conversation. Sometimes the next step is repeat bloods, sometimes a scan review, and sometimes discussion of a different screening or diagnostic route.
There is no single “right” response to screening information. Good counselling is about helping you understand the result, decide how much certainty you want, and choose the next step that fits your values.
Frequently asked questions
Common questions about first-trimester screening
What is the non-invasive prenatal test (NIPT)?
NIPT is a blood test from your arm. It looks at placental DNA in your bloodstream to estimate the chance of some common chromosomal conditions such as Down syndrome, trisomy 18, and trisomy 13. It is a screening test, not a diagnostic test.
What is the nuchal translucency (NT) scan?
The NT scan is a focused ultrasound in the 11 to 14 week window. It measures the fluid at the back of the baby’s neck and also reviews early anatomy. It can add useful information to a first-trimester screening pathway, but it is not the same as the later anatomy scan.
What does the blood test in combined screening actually measure?
In a combined screening pathway, a blood sample is taken from your arm. The lab measures pregnancy-related proteins and hormones in your blood, often markers such as PAPP-A and beta-hCG, and that information is interpreted together with the NT scan, your dates, and your age to estimate chance. The blood test itself does not put the pregnancy at risk.
What is the difference between a screening test and a diagnostic test?
A screening test tells you whether a condition looks lower chance or higher chance. A diagnostic test is used when you want much more certainty. Screening helps decide whether a further conversation is needed; diagnostic testing is used when you want a more definite answer.
What is chorionic villus sampling (CVS), and how is it different from amniocentesis?
Both are diagnostic tests. CVS usually happens earlier and takes a small sample from the placenta. Amniocentesis usually happens later and takes a small sample of the amniotic fluid. Which one is relevant depends mainly on timing and what question needs answering.
Do CVS and amniocentesis carry risk?
Yes. Because they are invasive tests, they do carry a small procedure-related risk, including miscarriage. That is why these tests are usually discussed carefully when a screening result is higher chance or when more certainty would meaningfully change what happens next.
Why don’t we just go straight to CVS or amniocentesis?
In most pregnancies that would mean using a more invasive test before safer screening options have been tried. Because NIPT is highly accurate for the common trisomies, it has in many pregnancies reduced the need to go straight to invasive testing as a first step. CVS and amniocentesis are still important, but they are usually reserved for pregnancies where that extra certainty would genuinely change what happens next.
Who performs CVS or amniocentesis?
If one of these diagnostic tests is chosen, it is arranged with an independent subspecialist outside my practice. These are focused invasive procedures and are usually done in a specialist fetal-medicine setting rather than in the rooms.
Can I choose not to do first-trimester screening?
Yes. Screening is optional. Some patients want as much information as possible, some prefer routine pregnancy care and the anatomy scan, and some choose a middle path. What matters is that the decision fits you.
Is age part of the screening result?
Yes. Maternal age is part of the way first-trimester screening algorithms estimate risk. That does not mean age is the only thing that matters, but it does mean the same scan or blood result may be interpreted differently at different ages.
Is NIPT always funded?
Not always. One practical drawback of NIPT is that it can be more expensive and is not always funded routinely. In some pregnancies, if the blood test, NT scan, or combined screening result comes back higher chance, a medical aid may then fund NIPT as a next screening step.
What can I do with the information if a result is higher chance or a condition is confirmed?
Different patients use the information differently. Some continue the pregnancy and use the result to plan better care, specialist review, delivery, or neonatal support. Some want diagnostic testing for more certainty first. Others want to discuss whether continuing the pregnancy is right for them, including the option of termination. The purpose of counselling is to help you understand the information and choose the path that fits you.
Next steps
Choose a screening pathway on purpose
The best screening pathway is the one that fits your timing, your questions, and what you would actually want to do with the result. If you want help working that through, the discussion is worth having before the window passes.