11-14 Weeks

The nuchal fold is a small skin fold at the back of your baby’s neck that can sometimes look a bit thicker if certain conditions (especially trisomy 21) are present.

It is usually measured at the detailed 18–21-week scan as one of several “soft markers” that can give extra information about your baby’s health.

In most pregnancies between 15 and 20 weeks, a nuchal fold measuring less than 6.0 mm is considered normal.

If your baby’s nuchal fold is 6.0 mm or more, your report will usually describe it as “increased” or “thickened”. On its own it is a soft marker, not a diagnosis, and many babies with a thick nuchal fold are born completely healthy.

If you already had a low-chance NIPT result, this is very reassuring because NIPT has a very high negative predictive value for Down syndrome (T21). In this situation, an isolated thick nuchal fold usually adds only a small extra concern.

You should still be offered a detailed expert scan of your baby by a fetal medicine specialist (in an FMU or a specialist private clinic). You may also be offered the option of an amniocentesis. This is a diagnostic test that looks directly at the baby’s chromosomes, but it is invasive and carries a small risk of miscarriage, so the pros and cons should be carefully discussed with you by a fetal medicine doctor.

You should be offered a detailed expert scan in a Fetal Medicine Unit (FMU) or with a private fetal medicine specialist to check the baby thoroughly, especially the heart and face. Depending on your previous screening, you may also be offered NIPT (if not already done) or diagnostic testing such as amniocentesis.

Usually, a follow-up scan is recommended to make sure the baby continues to look well and to exclude the small possibility of developing generalised skin swelling (oedema) or hydrops.

Not usually. Unlike an increased nuchal translucency (NT) in early pregnancy, which is clearly associated with congenital heart disease, the link between an increased nuchal fold and heart problems in babies without a chromosomal condition is less well documented and probably weaker.

However, a thick nuchal fold can sometimes be seen in babies with heart defects. For this reason, your baby’s heart should be examined very carefully by an expert – either as part of a detailed fetal medicine scan or in a separate specialist heart scan (fetal echocardiogram), depending on the pathway with your antenatal care provider.

Yes, image quality can be affected by your build and by the ultrasound equipment used. Using a high-quality scanner and having the nuchal fold measured by an experienced sonographer or fetal medicine specialist helps to reduce errors.

However, as with all screening tests, it is impossible to be completely certain whether the nuchal fold was truly increased on the first scan and has since normalised, or whether it was simply overestimated initially. Because of this, many fetal medicine specialists will still manage your pregnancy as having had an increased nuchal fold, even if the repeat measurement falls within the normal range. They may therefore offer you further screening with NIPT (if not already done) or discuss an invasive diagnostic test such as amniocentesis, which looks directly at the baby’s chromosomes but carries a small risk of miscarriage.

Yes. In some babies, the nuchal fold in the second trimester remains thick after an increased nuchal translucency (NT) was seen in the first trimester, and this combination is generally a less favourable sign.

If you have already had an invasive test (CVS or amniocentesis) and the results of rapid aneuploidy testing (QF-PCR) and chromosomal microarray (CMA) are normal, a persistently increased nuchal fold can raise the possibility of an underlying single-gene (monogenic) or other non-chromosomal condition, such as a RASopathy (for example, Noonan syndrome).

In this situation, more detailed genetic testing – such as exome sequencing or whole-genome sequencing (WGS) – may be very helpful, and referral to fetal medicine and clinical genetics for specialist counselling is usually recommended.

If you miss this window, you can no longer have the NT-based combined test, but you may be offered a later second-trimester blood test (the “quadruple test”), and you will still be offered the detailed 20-week anomaly scan with NF measurement.

It is important to understand that the quadruple test has limited value, and a significant proportion of babies with Down syndrome will not be identified by this screening. The second-trimester scan is very useful for detecting structural anomalies, particularly those associated with Edwards and Patau syndromes; however, it is relatively insensitive for Down syndrome on its own.

For this reason, many professionals will recommend proceeding with NIPT, which continues to work very well even at later gestations.

Yes. The measurement of NF is technically quite challenging and can change if the baby’s head and neck are extended or flexed, or if the baby is moving. This is why it should be done by an experienced sonographer or fetal medicine specialist, and sometimes repeated if the position is not ideal.

No. Nuchal translucency (NT) is a fluid space measured at the back of the neck in the first trimester (around 11–13 weeks).

The nuchal fold (NF) is a different measurement of the skin and underlying tissue at the back of the neck in the second trimester (around 18–21 weeks).

The nuchal fold is usually measured once and not routinely followed through the rest of the pregnancy. This is because this part of the baby’s neck naturally becomes thicker as the baby grows, so later measurements are harder to interpret. There are no good studies on nuchal fold measurements after 20 weeks, and the commonly used 6.0 mm cut-off has not been clearly validated beyond this stage.

However, some fetal medicine specialists may suggest a follow-up scan to make sure the baby continues to look well and to exclude the very small possibility of generalised skin swelling (oedema) or hydrops. These complications are extremely rare, and in some babies a borderline or slightly increased nuchal fold can look normal on a repeat scan, especially if the first measurement was technically difficult.

No, they are not the same. They are only similar in that both are found at the back of the baby’s neck.

‍Increased nuchal fold (NF) is a thickening of the skin and tissue at the back of the neck, usually measured around 18–21 weeks as a soft marker.

‍Cystic hygroma is a large fluid-filled space or sacs at the back of the neck, often seen earlier in pregnancy and more strongly associated with chromosomal or genetic conditions and lymphatic problems.

They look different on ultrasound, have different causes and risks, and are managed in different ways. If a cystic hygroma is suspected, you should be referred to a fetal medicine specialist for detailed assessment and counselling.

A clearly increased nuchal fold is not very common, but it is one of the more frequent “soft markers” found at the mid-pregnancy scan.

Most women with this finding will still go on to have a healthy baby, especially if nothing else is seen on the scan and the results of NIPT are low chance.

It is a difficult decision, and it should be made together with your antenatal care team, ideally a fetal medicine specialist, rather than on your own. The recommendation will depend on several factors: your age, your earlier screening results (especially NIPT), how increased the nuchal fold is, and whether any other findings are seen on the scan.

Many parents in this situation choose to have NIPT first (if not already done), because a low-risk NIPT result makes Down syndrome very unlikely. Others prefer to go straight to a diagnostic test such as amniocentesis for a definite answer, even though it is invasive and carries a small risk of miscarriage.

Always discuss your options in detail with a fetal medicine doctor, who can explain the pros and cons in your specific case.