Nuchal Translucency Scan: What It Measures and What Results Mean

✓ This content has been medically reviewed by an obstetrician and gynaecologist
Written & medically reviewed by: Op. Dr. Ayşet Jane Özcan, Obstetrics & Gynaecology Specialist
Istanbul Faculty of Medicine · Medical Park Bahçelievler · TJOD and TSRM member
Last updated: 15 October 2026 · Last medical review: 15 October 2026

If you are between 11 and 14 weeks pregnant, you will probably be offered a scan that measures something called the nuchal translucency — a thin layer of fluid at the back of your baby's neck. It is one of the first moments in pregnancy when a measurement is taken and a number is produced, and for most people it is also the first time they are handed a probability rather than an answer. That combination tends to generate more worry than the test itself warrants.

This article explains what the measurement is, why the 11 to 13+6 week window exists, how the number is taken and what makes it valid, how it is combined with two blood markers into a single estimated chance, and how to read that chance when it arrives. It also covers what happens if the result comes back higher than the cut-off, what is looked for when the nuchal measurement is increased but the chromosomes are normal, and — just as importantly — the questions this scan is not able to answer.

What the Nuchal Translucency Scan Is

The nuchal translucency scan is an ultrasound performed in the first trimester that measures a small, fluid-filled space under the skin at the back of your baby's neck. Every baby has this space. The scan is not looking for whether the fluid is there, but for how thick it is compared with what is expected for a baby of that size.

"Nuchal" refers to the nape of the neck, and "translucency" describes how the fluid appears on the screen: a clear black band sitting between two brighter lines, the skin on one side and the soft tissue over the spine on the other. The sonographer measures the widest part of that band in millimetres, recorded to one decimal place. A typical report will read something like "NT 1.6 mm".

The reason this particular measurement is useful is statistical rather than anatomical. Fluid gathers at the back of the neck in all babies during early development and, in most, drains away through the lymphatic system by around 14 weeks. When the fluid layer is thicker than expected, it is more often found alongside chromosomal conditions — most commonly trisomy 21 (Down's syndrome), and also trisomy 18 (Edwards' syndrome) and trisomy 13 (Patau's syndrome) — and alongside congenital heart defects and certain genetic syndromes.

Two things follow from that, and they matter more than any single number on your report. The first is that nuchal translucency is a marker, not a diagnosis. A thicker measurement does not mean a baby has a condition, and a thin one does not prove that it does not. The second is that the measurement is almost never interpreted on its own. In routine care it is combined with your age, the pregnancy's gestational age and two hormones measured in your blood, and what comes out is a single estimated chance.

Why it is offered at all

First-trimester screening exists so that you can find out, early and with nothing more than a scan and a blood test, whether your pregnancy sits in a group with a higher or a lower chance of these conditions — and then decide for yourself whether you want more information. It is offered to everyone, at any age. It is entirely optional, and choosing not to have it does not change any other part of your antenatal care.

When It Is Done: the 11 to 13+6 Week Window

The nuchal translucency scan is done between 11 weeks 0 days and 13 weeks 6 days of pregnancy. In practice the window is defined not by dates but by the baby's size: the crown-rump length, measured from the top of the head to the bottom of the back, must be between about 45 mm and 84 mm.

There is a reason for a window rather than a single date, and a separate reason for each of its edges.

Why not earlier than 11 weeks

Before 11 weeks the baby is simply too small for the measurement to be reproducible. The calipers that mark the edges of the fluid layer have to be placed within a fraction of a millimetre, and at a crown-rump length under 45 mm that precision is not achievable. Several structures the sonographer also checks at this appointment — the skull bones, the midline of the brain, the abdominal wall, the bladder — are not yet developed enough to be assessed.

Why not later than 13+6

After about 14 weeks the nuchal fluid normally drains away as the lymphatic system matures. A measurement taken later therefore loses most of its ability to distinguish between pregnancies: a thin reading at 15 weeks is expected in almost everyone and tells you very little. The two blood markers used alongside the scan also behave differently as gestation advances, and the calculation they feed into is calibrated for this window only.

If you are uncertain of your dates, the scan sorts that out at the same appointment. The crown-rump length sets the gestational age, and the whole risk calculation is then based on that corrected dating rather than on your last menstrual period. In pregnancies conceived through assisted reproduction, dating comes from the day of egg collection or embryo transfer and is already precise.

If you miss the window

It happens — a late booking, a holiday, a baby lying awkwardly through two appointments. Once the window closes, nuchal translucency screening is no longer possible, but other options remain. A second-trimester blood test, sometimes called the quadruple test, is offered in some services from around 14 to 20 weeks and screens for Down's syndrome using maternal blood alone. Non-invasive prenatal testing on a blood sample can also be arranged later in pregnancy. The detailed anomaly scan in the second trimester is unaffected and goes ahead as normal.

• Book the scan at your first antenatal appointment, so the timing is not left to chance
• Allow 20 to 30 minutes, and be prepared to be asked to return if the baby will not move into position
• You do not need to fast; a partly full bladder can help the view early in the window
• Bring any earlier scan reports and, if you know it, the date of your last period
• Ask whether the blood sample is taken on the day or at a separate, earlier visit

What Else Is Checked at the Same Appointment

The nuchal measurement is only part of what this appointment is for. By the time you leave, a well-conducted first-trimester scan will usually have established several things that are difficult or impossible to establish later.

Whether the pregnancy is ongoing, and how many babies there are. The heartbeat is confirmed and the number of babies counted. If there is more than one, this is the single best moment in the whole pregnancy to determine chorionicity — whether the babies share a placenta. That distinction drives how the rest of the pregnancy is monitored, and after about 14 weeks it becomes much harder to judge with confidence.

Accurate dating. Crown-rump length in the first trimester is the most reliable way to date a pregnancy, and that date then governs the timing of every later test and scan.

An early look at the anatomy. This is not the anomaly scan, but a good deal is already visible at 12 weeks: the skull and the shape of the brain, the abdominal wall, the stomach and bladder, the spine and the four limbs. Some significant structural problems — absence of the skull vault, an abdominal wall defect, a markedly enlarged bladder — can be identified at this stage rather than months later.

The uterus and ovaries. Fibroids, ovarian cysts and the apparent position of the placenta are noted, on the understanding that placental position is reassessed later in pregnancy.

First-trimester pre-eclampsia assessment

Many services now use the same 11 to 13+6 week visit to estimate the chance of early pre-eclampsia, combining your medical history, your blood pressure, blood flow in the uterine arteries measured on the scan and, in some units, a placental growth factor blood test. This is a separate calculation from the chromosomal one and it leads to a different action: where the estimated chance is high, low-dose aspirin started before 16 weeks is recommended. It is worth reading separately about the signs and risks of pre-eclampsia so that you know what to watch for later on.

One incidental finding deserves a mention here, because it often causes confusion weeks later. If the PAPP-A hormone measured for the combined test comes back low but the chromosomes turn out to be normal, that pattern is associated with how well the placenta is working, and some units respond by adding extra growth scans in the third trimester. A low PAPP-A on its own is not a diagnosis of anything. It is a reason for closer watching.

How the Measurement Is Taken

The measurement is taken through the abdomen in most cases, with gel and a standard ultrasound probe, in the same way as any other pregnancy scan. In a minority of women — usually where the uterus is tilted backwards, the abdominal wall is thicker, or the pregnancy is at the very start of the window — a transvaginal scan gives a clearer image and is offered instead. Neither approach is uncomfortable beyond mild pressure, and neither carries a risk to the pregnancy. If you have not had a scan before and want to know what the experience is like in general, our guide to what a pelvic ultrasound shows and what to expect covers the practical side.

What makes a nuchal measurement valid is not the machine but the technique. There is an internationally agreed set of criteria, and sonographers who perform the measurement are trained and audited against them.

• The baby is shown in a true mid-line profile view of the face, not turned to one side
• The image is magnified so that the head and upper chest fill the screen
• The neck is in a neutral position — neither tipped back nor tucked into the chest, as both alter the reading
• The thin amniotic membrane is clearly distinguished from the baby's skin, which is easy to confuse
• The calipers are placed on the inner borders of the clear space, at its widest point
• Several measurements are taken, and the largest valid one is used

Those conditions are the reason the appointment can take longer than you expect. A baby who is curled up, lying face-down or simply refusing to move will not give a valid image, and no amount of pressing with the probe will produce one. You may be asked to walk around, empty your bladder, cough, or come back another day. This is routine, and it is not a sign that anything is wrong.

Because the measurement is technique-dependent, small differences between operators are real. This is one reason risk calculation software works with the measurement relative to the baby's size rather than treating a raw millimetre value as absolute, and why services run quality audits on the distribution of each sonographer's results.

Ultrasound at the settings used for obstetric imaging is considered safe, and the nuchal scan is performed mainly in ordinary two-dimensional imaging mode. Exposure is kept to what the clinical question requires.

What Counts as an Increased NT Measurement

There is no single millimetre value that separates normal from abnormal across the whole window, because nuchal translucency naturally increases as the baby grows. A measurement of 2.2 mm at a crown-rump length of 45 mm is not the same finding as 2.2 mm at 84 mm. Interpretation is always relative to size, and this is handled by the software rather than by eye.

With that caveat, some reference points are useful:

• Most measurements across the window fall below about 2 mm
• The 95th centile rises from roughly 2 mm at the start of the window to around 2.7 mm at the end
• The 99th centile sits at about 3.5 mm and changes very little with the baby's size
• 3.0 mm and 3.5 mm are the thresholds most services use to trigger additional assessment
• A measurement of 3.5 mm or more usually prompts referral to a fetal medicine specialist regardless of what the combined risk number says

The relationship between measurement and chance is continuous, not a cliff edge. There is no point at which a measurement suddenly becomes dangerous. The chance of an underlying chromosomal or structural problem rises steadily as the measurement increases, which is why a reading of 3.6 mm and a reading of 6 mm are approached with very different degrees of concern even though both would be described as increased.

The appearance of the fluid matters as well as its depth. A thickened layer divided by septa, often described as a cystic hygroma, carries a stronger association with chromosomal conditions and with heart defects than a smooth collection of the same thickness, and it is managed accordingly.

If your measurement is 2.4 mm or 2.8 mm and your combined result comes back as lower chance, that measurement is not an abnormal finding sitting unaddressed in your notes. It has already been taken into account in the calculation. The number on the ultrasound report is an input, not a verdict.

How NT Combines With Blood Tests Into One Risk Result

The combined test takes a starting chance and adjusts it. The starting point — what statisticians call the background or prior risk — comes from your age and the gestational age of the pregnancy, because the chance of a chromosomal trisomy rises with maternal age and because the chance changes as pregnancy advances. That starting figure is then multiplied up or down according to three measurements: the nuchal translucency, and two substances in your blood.

The two blood markers

Pregnancy-associated plasma protein A (PAPP-A) and free beta human chorionic gonadotrophin (free beta-hCG) are both produced in pregnancy and both vary widely between healthy pregnancies. Neither is interpreted as a raw laboratory value. Each is converted into a multiple of the median — how far it sits above or below the typical value for that exact gestational age — so that a result from 11 weeks can be compared fairly with one from 13 weeks.

In pregnancies affected by trisomy 21, free beta-hCG tends on average to be higher than expected and PAPP-A lower, alongside a thicker nuchal translucency. In trisomy 18 and trisomy 13, both blood markers tend to be low. These are tendencies across populations, with a great deal of overlap between affected and unaffected pregnancies, which is precisely why no single marker is ever used alone.

The adjustments that are applied

Before the final figure is produced, the software corrects for factors known to shift the markers independently of the baby: your weight, ethnic background, smoking status, pre-existing diabetes, whether the pregnancy was conceived through assisted reproduction, whether you are carrying more than one baby, and any previous affected pregnancy. These corrections are not cosmetic. Omitting them produces a meaningfully wrong number, which is why the request form asks for details that can seem irrelevant.

The output is usually not one number but two or three: a chance for trisomy 21, and a combined or separate chance for trisomies 18 and 13. You can be below the cut-off for one and above it for another, and that is not a contradiction.

Extra markers used in specialist units

Some centres add further first-trimester ultrasound markers to refine the calculation: whether the nasal bone is visible, the pattern of blood flow through the ductus venosus, and whether there is backflow across the tricuspid valve of the heart. Each requires additional training and accreditation, and they are not part of every routine service. They are most often used when an initial combined result sits close to the cut-off.

Taken together, the combined test identifies the majority of pregnancies affected by Down's syndrome, while placing a small proportion of entirely unaffected pregnancies in the higher-chance group. Both halves of that sentence matter: it is good enough to be worth offering, and imperfect enough that it can never be the final word.

How to Read a Risk Result Like 1 in 250

A result of 1 in 250 means this: if 250 pregnancies had exactly the same combination of maternal age, gestational age, nuchal measurement and blood results as yours, one of them would be expected to be affected and 249 would not. It is a statement about a group of pregnancies like yours. It is not a statement that your baby is partly or probably affected.

The most common misreading is the direction of the number. A larger second number means a lower chance. One in 1,500 is a lower chance than one in 150. If you are comparing two results, make sure you are comparing the denominators the right way round.

Where the cut-off comes from

Screening services draw a line and call results on one side "higher chance" and on the other "lower chance". A commonly used cut-off is 1 in 150, but it varies between services — ask which one applies to you. A line has to be drawn somewhere for a service to function, but it is an administrative convention, not a biological boundary. A result of 1 in 148 and a result of 1 in 155 describe near-identical pregnancies that have been sorted into different categories by a few decimal places in a formula. If your result sits close to the cut-off on either side, say so when you discuss it, because it changes how much weight the category deserves.

What the number does not tell you

It says nothing about severity. There is no sense in which 1 in 20 implies a more significantly affected baby than 1 in 200; the figure describes likelihood only. It does not cover conditions the test does not screen for. And a lower-chance result is not a guarantee. The combined test detects most — but not all — pregnancies affected by Down's syndrome; in the order of one in ten affected pregnancies will return a lower-chance screening result, which is why a lower-chance result reduces the chance rather than excluding the condition.

That residual chance is worth understanding properly, because it is easy to overstate in either direction. Lower-chance results are by far the most common outcome of screening, so even a small residual chance adds up to a meaningful number of babies when you look at a whole population of screened pregnancies. For your own pregnancy, though, a lower-chance result has genuinely moved the chance downwards — it has not merely relabelled it.

One practical detail is worth asking about. Some laboratories report the chance as it stands at the time of the test, and others report the chance at term. The two figures differ, and knowing which one you are holding prevents confusion if you compare reports or look up what other people were told.

Finally, the word "risk" does a lot of unhelpful work here. Services increasingly prefer "chance", because risk implies something to be avoided whereas the result is simply information. How you respond to 1 in 250 is not determined by the number itself. Some people find it reassuring enough to stop there. Others want certainty and go on to a diagnostic test. Both are reasonable responses to the same figure, and neither is the wrong one.

If the Chance Is Higher: NIPT, CVS and Amniocentesis

A higher-chance result is the beginning of a conversation, not the end of one. Nothing has to be decided on the day. You should be offered an appointment with someone trained to explain the result — a fetal medicine specialist, a clinician experienced in prenatal screening, or a genetic counsellor — and from there three broad paths are open: no further testing, a second and more accurate screening test, or a diagnostic test.

Non-invasive prenatal testing (NIPT)

NIPT analyses fragments of placental DNA circulating in your bloodstream. It needs only a blood sample from your arm, can be done from 10 weeks, and carries no risk to the pregnancy. For trisomy 21 it is considerably more accurate than the combined test, and it performs well for trisomies 18 and 13.

It nevertheless remains a screening test. A result reported as "high probability" should be confirmed by a diagnostic test before any irreversible decision is made, because a proportion of such results are not confirmed — most often because the placenta carries a chromosomal change that the baby itself does not. A small number of samples return no result at all, usually because too little placental DNA is present; this is more likely very early in pregnancy and at higher body weight, and a repeat sample often resolves it.

There is one situation in which NIPT is usually not the right next step: when the nuchal translucency is 3.5 mm or more, or a structural abnormality has already been seen. In those cases the concern extends well beyond the three common trisomies, and a diagnostic test with detailed genetic analysis gives information that NIPT is not designed to provide.

Chorionic villus sampling (CVS)

CVS samples placental tissue, either through the abdomen with a fine needle or through the cervix with a thin catheter, always under continuous ultrasound guidance and usually with local anaesthetic. It can be performed from 11 weeks. The procedure itself takes a few minutes, and most women describe period-like cramping afterwards.

Amniocentesis

Amniocentesis takes a small sample of the fluid surrounding the baby, using a fine needle through the abdomen under ultrasound guidance, from 15 weeks onwards. It is the alternative when the pregnancy is already past the CVS window, or when a CVS result needs clarifying.

Both are diagnostic: they examine the baby's own chromosomes and give a definite answer rather than a probability. Both carry a small risk of miscarriage, conventionally quoted as below 1 in 100 and lower than that in many present-day series. Anti-D is usually given afterwards if your blood group is rhesus negative.

What the laboratory does with the sample

A rapid test for the common trisomies usually reports within a few working days. A fuller analysis — a chromosomal microarray, which detects missing or duplicated segments too small to see on a standard karyotype — takes longer, typically two to three weeks. It is worth asking at the outset which analyses have been requested on your sample, because the waiting time you are quoted depends on which of them the result is being held for.

• Ask what each test can and cannot detect, and how long the result will take
• Ask who will give you the result, and how — by telephone or in person, and on which day
• Ask what the plan would be for each possible answer, before you agree to the test
• Take someone with you, and write the numbers down during the conversation
• Remember that you can pause at any point; declining further testing is a legitimate choice

After CVS or amniocentesis, contact your doctor or the clinic where you are being followed without delay if you have heavy bleeding, a leak of fluid from the vagina, a fever, severe or persistent abdominal pain, or regular contractions. Light spotting and mild cramping for a day or so are common; anything beyond that should be assessed. Our guide to bleeding during pregnancy sets out which patterns of bleeding need urgent attention at different stages.

Increased NT With Normal Chromosomes: What Else Is Checked

When the nuchal measurement is increased but chromosome testing comes back normal, the question changes. It is no longer about trisomies. It becomes a question about the heart, about genetic conditions a chromosome test does not look for, and about how the fluid itself behaves over the following weeks. Most of these pregnancies proceed without a problem, and the reassurance builds as each successive check comes back normal.

The heart

Congenital heart defects are the most important association with an increased nuchal translucency and normal chromosomes. For this reason a detailed fetal echocardiogram is arranged, usually at around 18 to 22 weeks, and sometimes an earlier specialist cardiac view at 15 to 16 weeks where the measurement was markedly increased. This is a dedicated examination of the heart's chambers, valves and great vessels, performed by someone with specific training, and it goes well beyond the cardiac views included in a routine anomaly scan.

Genetic conditions beyond the chromosomes

A standard karyotype counts and inspects whole chromosomes. A chromosomal microarray looks for much smaller deletions and duplications, and is the preferred analysis on an invasive sample when the nuchal measurement is increased. If that too is normal, attention turns to single-gene conditions recognised to present with increased nuchal fluid — Noonan syndrome and the related group of disorders are the classic examples — and targeted gene testing or exome sequencing may be offered through a fetal medicine or clinical genetics service. These tests are not a routine next step for every increased measurement; they are considered where the fluid is markedly increased, where it persists, or where other findings point in that direction, and they are discussed with you before any sample is sent.

The detailed anatomy

A thorough anomaly scan at 18 to 22 weeks is essential rather than optional in this situation. Conditions associated with increased nuchal fluid include skeletal dysplasias, congenital diaphragmatic hernia and disorders of fetal movement, and several of these declare themselves only in the second trimester.

Watching the fluid itself

The nuchal fluid is re-examined at subsequent scans. In most pregnancies it resolves quietly and nothing more is heard of it. If instead it persists as generalised swelling at the neck, or if fluid begins to collect in the chest, abdomen or skin elsewhere, that pattern is taken seriously and prompts further investigation, including testing for congenital infection in selected cases.

When chromosomes and microarray are normal, the detailed scan is normal, the heart is structurally normal and the nuchal fluid has resolved, the outlook for the pregnancy is generally good, and in many units the only lasting change is a plan for growth monitoring and a paediatric check after birth. That sequence of normal results, each building on the last, is the proper answer to the anxiety an increased measurement creates — not a single number offered on the day of the scan.

What the Nuchal Translucency Scan Cannot Tell You

Being clear about the limits of this scan prevents two opposite mistakes: treating a lower-chance result as a clean bill of health, and treating a higher-chance result as a diagnosis.

• It cannot diagnose anything. Only a sample of the baby's own cells, from CVS or amniocentesis, can do that
• It does not screen for all chromosomal conditions, and it does not look for the great majority of single-gene or inherited disorders
• It does not detect most structural anomalies. That is the work of the anomaly scan in the second trimester, and a normal first-trimester scan is no substitute for it
• It cannot exclude a heart defect. A normal nuchal measurement lowers the chance but does not rule one out
• It says nothing about severity, or about what a child's abilities and life will be like
• It does not screen for autism, cerebral palsy or learning difficulty in general, despite how often that is assumed
• It is not valid after 14 weeks, because in almost all babies the fluid has normally drained away by then; where fluid instead persists, it is assessed as nuchal oedema at later scans rather than as a nuchal translucency measurement
• It is operator-dependent, which is why accredited technique and ongoing audit matter so much

There is also something it cannot tell you reliably that people frequently ask about at this appointment: the baby's sex. The external genitalia are forming at 12 weeks but are not reliably distinguishable, and any impression offered at this stage should be treated as provisional.

Finally, a lower-chance result does not shorten or simplify the rest of your antenatal care. The anomaly scan, blood pressure and urine checks, blood tests, growth assessment and attention to fetal movements all continue exactly as they would otherwise.

Twins, IVF Pregnancies and Other Special Situations

Several common circumstances change how the scan is performed or how the result is calculated. It helps to know in advance if one of them applies to you.

Twins and higher multiples

Each baby has its own nuchal measurement taken. How the result is then reported depends on chorionicity, which is established at this same scan. In dichorionic twins, where each baby has its own placenta, a separate chance is calculated for each. In monochorionic twins, who share a placenta and are genetically identical, a single chance is calculated for the pregnancy using the average of the two measurements. The blood markers are less discriminating in twin pregnancies, so the scan contributes proportionally more to the final figure.

There is a second reason the measurements matter in monochorionic twins. A marked difference in nuchal translucency between the two babies can be an early indicator of twin-to-twin transfusion syndrome developing later, and it prompts a schedule of closer surveillance regardless of what the chromosomal result shows.

Pregnancies conceived through assisted reproduction

Dating is more precise after IVF, because the date of egg collection or embryo transfer is known exactly, and that removes one source of error from the calculation. PAPP-A levels tend to run lower in pregnancies conceived through IVF, and risk software applies a correction for this. Make sure the laboratory form records that the pregnancy was conceived with assistance, because an uncorrected result will read as a higher chance than it should. Where donor eggs were used, the age used for the background chance is the donor's age at collection, not yours.

When one of a pair has stopped developing

If a twin pregnancy has reduced to one, the blood markers can be distorted for weeks afterwards, and non-invasive prenatal testing may also be unreliable. In that situation the ultrasound markers carry more weight, and this should be discussed before relying on any biochemical result.

Practical difficulties with the view

A retroverted uterus, fibroids, previous abdominal surgery or a higher body mass index can all make a valid mid-line image harder to obtain. None of these prevents the scan; they make a transvaginal approach or a second appointment more likely. Being asked to come back is a sign that the sonographer is holding to the standard, not a sign that something has been found.

Deciding Whether to Have the Scan, and When to Seek Care

Screening is a choice, and declining it is a reasonable one. Some people want every piece of information available to them; others know that a probability would only generate anxiety without changing anything they would do. Neither position is more responsible than the other, and declining has no effect on the rest of your care. In many services you can also accept the scan for dating and early anatomy while declining the risk calculation — it is worth asking whether that is possible where you are booked.

The question worth answering before the appointment, rather than after the result, is a simple one: what would I do with this information? If a higher chance would lead you to want a diagnostic test, it helps to know that beforehand. If it would not change anything, that is equally worth knowing. Where you have a partner, this is a conversation to have together and in advance, because it is a far harder conversation to begin on the day a result arrives.

Questions worth asking at the appointment

Which conditions does this test screen for in the service caring for me? When exactly is my window, and when is the blood sample taken? How and when will I get the result, and who will explain it to me? What cut-off is used here, and is the chance reported as it stands now or at term? And if the result comes back as higher chance, what would be offered next, and how quickly?

When to seek care

Around the time of the scan, the general warning signs of early pregnancy apply as they always do. Contact your doctor or the clinic where you are being followed promptly if you have vaginal bleeding, severe or one-sided abdominal pain, shoulder-tip pain, fainting, a fever, or vomiting so persistent that you cannot keep fluids down. None of these are related to having had a nuchal scan — they are the ordinary reasons to be seen in the first trimester, and they do not become less important because a scan looked normal.

After an invasive test, the specific warning signs described earlier apply: heavy bleeding, loss of fluid, fever, severe pain or contractions.

Whatever you decide about screening, the shape of the pregnancy that follows is the same — regular pregnancy follow-up appointments, the second-trimester anomaly scan, blood pressure and urine monitoring, growth assessment where it is indicated, and a clear route to contact someone between appointments. A screening result is one piece of information gathered along the way. It is not the thing the pregnancy turns on.