How Much Shlould Mesure the Baby Neck at Week 12

Nuchal translucency (NT) is a drove of fluid nether the skin at the back of your babe's neck. The amount of fluid is measured during an NT ultrasound scan:

• between eleven weeks and 13 weeks plus six days of pregnancy
• or when your baby measures between 45mm and 84mm, crown to rump
  (ASUM 2018, DH 2018, Nicolaides 2011, PHE 2018, UK NSC 2016)

All developing babies have some fluid at the dorsum of their neck. But many babies with Downwards syndrome or other chromosomal weather take an increased amount (ASUM 2018, PHE 2018).

That'south why the NT browse is used to assistance screen for Downward syndrome.

Why might I have a nuchal translucency scan?

All significant women in Australia are offered an NT scan, to assist appraise whether or non their babies are likely to have Down's syndrome (DH 2018, RANZCOG 2018).

Every adult female has a run a risk of giving birth to a infant with Down syndrome. The chance increases every bit you get older.

A screening examination tries to go a clearer interpretation of how likely it is that your baby has Down's syndrome. It tin can't tell you for sure.

If the results show that your infant has a high take a chance of having the condition, it doesn't mean they definitely have Down syndrome. And if the browse says your baby has a low chance, information technology doesn't definitely mean they don't have Down syndrome.

For instance, if the outcome of your scan shows that you take a one in one,000 gamble, this means that for every ane,000 babies with your level of likelihood, one will have Down syndrome. A chance of more than one in 300 is generally considered high (MCRI 2018, RANZCOG 2018), because it means that for every 300 babies with your level of likelihood, 1 volition have Down syndrome.

Diagnostic tests, such as chorionic villus sampling (CVS) and amniocentesis, tin can say for certain whether or not your baby has Down's syndrome or another chromosomal status.

But diagnostic tests practice carry a pocket-sized risk of miscarriage. Because of this, your doctor will desire you to have a screening examination before they'll offer you lot a diagnostic test.

The screening test combines the NT scan outcome, with a blood examination and other factors, such every bit your age. The exam is designed to requite you equally much information equally possible, and so you lot can make up one's mind whether or not to go ahead with a diagnostic test.

Practice I have to have an NT scan?

Although your caregiver volition offer you an NT browse, it'south your selection whether to have one.

But even if you don't desire your infant screened for Down syndrome, it's yet a expert idea to have the browse. During the scan, the sonographer will likewise check the overall wellness of your baby, whether yous're having twins or more, how your baby is growing and whether they may have whatever other weather.

How is the nuchal translucency scan performed?

An NT ultrasound scan must take place at a detail fourth dimension in your pregnancy. This is between eleven weeks and 13 weeks plus six days, or when your baby'southward crown rump length (CRL, the length from his head to bottom) is between 45mm and 84mm. Information technology'southward oftentimes combined with your dating browse.

It's difficult to do the browse before eleven weeks because your baby is however so small. It would also exist also early to combine information technology with your first trimester blood test.

Information technology's likewise late to do the NT browse after 14 weeks, because whatever excess nuchal fluid may be absorbed by your babe's developing lymphatic organisation.

The scan is usually washed through your belly using normal ultrasound equipment. The person carrying out the browse (sonographer) volition put some gel on your belly and move a hand-held device (transducer) over your pare. It shouldn't injure, though you may feel some pressure every bit the sonographer presses the transducer into your skin to get a good view.

Information technology's non ever possible for the sonographer to go a good enough view with the transducer. This is particularly likely if your uterus (womb) is deep in your pelvis or tilts backwards, or if yous're overweight. If this is the example, the sonographer volition enquire your permission to carry out a vaginal scan. It's safe for yous and your baby, and shouldn't be as well uncomfortable.

To engagement your pregnancy accurately, your sonographer volition measure your baby from the top of the head to the bottom of the spine. They'll then measure the width of the nuchal fluid at the back of your baby's neck. The peel will appear equally a white line, and the fluid under the pare volition await blackness.

You lot'll usually be able to see your infant's head, spine, limbs, easily and feet on the screen. Your sonographer will be able to rule out some major abnormalities, such equally problems with your baby's abdominal wall, stomach and skull.

Yous'll also be offered a more detailed anomaly scan at about 20 weeks. Past this time, the sonographer can encounter your baby's features better, so the anomaly scan gives a clearer idea of how your infant is developing.

It may help if your partner or a friend goes with you to the scans, to share the experience and be with you when you get the results. It's best not to bring toddlers or young children. If you don't have any option, though, you should also bring a support person to intendance for your child or take them for a walk if they get restless during the scan, which tin take thirty to 45 minutes.

How accurate is the nuchal translucency scan?

The NT browse on its own picks up about 77 per cent of babies with Down syndrome (Nicolaides 2011).

Sometimes, though, a scan tin propose that a babe has a high gamble of having Down syndrome, even though the likelihood is actually low. This is called a false positive.

The faux-positive rate for an NT browse is v per cent (FMF nd, Nicolaides 2011). This ways that one woman in xx is wrongly given a high-chance calculation based just on her NT scan results.

Just the NT browse is rarely done alone. Combining an NT scan with a blood examination gives a more accurate event. The blood test measures the levels of the hormone free beta-hCG and the protein PAPP-A. Babies with Down syndrome tend to accept high levels of hCG and depression levels of PAPP-A.

When the NT scan is combined with this blood test, the detection rate increases to 90 per cent (Nicolaides 2011). This is called the combined examination.

The combined test too takes into account factors such every bit your age and ethnicity, and whether you take diabetes or have ever had a kid with Down syndrome. These factors all touch on the likelihood that your electric current babe has a chromosomal status. Some ultrasound providers may besides add other ultrasound findings to the calculations, such every bit whether they can run into a nasal bone, or certain blood menstruum changes within your infant'southward heart.

The well-nigh accurate screening test is a non-invasive prenatal test (NIPT), which is just available privately. It has a detection rate of 99 per cent (Nicolaides et al 2013). NIPT has a false-positive rate of 0.one per cent, which means it gives fewer false-positive results than the combined test.

What is a normal nuchal translucency measurement?

An NT of less than iii.5mm is considered normal when your baby measures between 45mm and 84mm from crown to rump (PHE 2018).

The NT normally grows in proportion with your babe (Nicolaides 2011). The images below give an idea of what dissimilar levels of NT wait similar.

Nuchal translucency of i.3mm

Nuchal translucency of 2.9mm

A baby with an NT of i.3mm is within the normal range.

The babe with an NT of 2.9mm is too within the limit of normal range. Anything less than 3.5mm is considered inside the normal range, meaning the likelihood of Down's syndrome is low (Nicolaides 2011).

Nuchal translucency of 6mm

Every bit the NT increases, so does the chance of Downwards syndrome and other chromosomal abnormalities. An NT of iii.5mm or more than is in the high range.

So the infant with an NT of 6mm has a high chance of having Down syndrome, equally well every bit other chromosomal abnormalities and middle problems (Chudleigh et al 2016, Nicolaides 2011). Simply one in 100 babies accept an NT of 3.5mm or more than, then it's uncommon.

But even a normal NT measurement would need to be considered with your claret exam results and other factors, such equally your age. Your sonographer will enter your NT measurement, blood exam results and other factors into a database to generate a more accurate estimation of the risk of Down's syndrome.

What if I take a high chance of Down's syndrome?

Most women given a high adventure (generally higher than 1 in 300 (MCRI 2018, RANZCOG 2018)) will go on to have a babe without Down syndrome. Even with a hazard as loftier equally one in five, at that place's a four out of v adventure that your baby doesn't have Down syndrome. All the same, it's natural to feel anxious and unsure of what to do.

If you fall into the loftier-chance category, your caregiver may refer you to a specialist doctor or a genetic counsellor (DH 2018).

During pregnancy, the just mode to know for sure that your babe has Down syndrome or another chromosomal abnormality, is to have a diagnostic examination, such as CVS or amniocentesis. Equally these tests carry a pocket-sized risk of miscarriage, this decision tin be difficult, only you don't have to decide in a hurry.

One advantage of the combined examination is that you have it early in your pregnancy, which gives you lot time to decide your side by side steps. It's possible to have a CVS and get the result while you're still in your first trimester. If y'all're unsure, you can expect until 15 weeks and take an amniocentesis.

Your caregiver volition thoroughly explain these diagnostic tests (DH 2018, RANZCOG 2018). You'll also have the adventure to talk about what whatsoever abnormalities could mean for the hereafter wellness and development of your babe.

If you're given a high-chance result from your combined test, your physician or midwife may suggest doing a non-invasive prenatal testing (NIPT) (RANZCOG 2018).

NIPT is a more accurate screening test than the combined examination (Great britain NSC 2016), and if your effect shows a low likelihood of Down syndrome, it's very unlikely your babe has the condition. So you may only need to consider a CVS or amniocentesis if the NIPT result confirms that your babe has a very high chance of a chromosomal abnormality. NIPT is currently simply bachelor privately.

Some parents who discover that their unborn infant is afflicted by abnormalities may consider the difficult decision virtually whether to end the pregnancy. But you should never be expected to consider ending your pregnancy based on NT scan findings alone. E'er ask for a 2d opinion if you lot're in any way unhappy with the communication you lot're given.

Volition I exist given a likelihood level for whatsoever other abnormalities during my NT scan?

Your NT scan results will as well assistance work out your baby'due south chance of having Edwards syndrome and Patau syndrome, which are two other chromosomal abnormalities (PHE 2020).

These conditions are much rarer than Down syndrome, and, sadly, most affected pregnancies end in miscarriage. Babies with these conditions normally also take abnormalities that can be seen on your NT scan or your anomaly scan at well-nigh 20 weeks.

More than data

• Read more nigh screening for Down syndrome.
• Find out about non-invasive prenatal testing (NIPT).
• Learn more near CVS and amniocentesis.

Images by BabyCenter

References

ASUM. 2018. Guidelines for the performance of first trimester ultrasound. Australasian Society for Ultrasound in Medicine, Guideline G02. www.asum.com.au [Accessed Feb 2020]

Chudleigh T, Smith A, Cumming S. 2016. Obstetric and gynaecological ultrasound eastward-Book: how, why and when. quaternary ed. Elsevier: London, 123-59

DH. 2018. Pregnancy care: clinical practice guidelines. Updated June 2019. Department of Health. Canberra: Section of Health. www.health.gov.au [Accessed Feb 2020]

FMF. nd. Nuchal translucency scan. The Fetal Medicine Foundation, Certificates of Competence. fetalmedicine.org [Accessed Feb 2020]

MCRI. 2018. Your choice: prenatal screening tests in pregnancy. Murdoch Children's Research Institute. world wide web.mcri.edu.au [Accessed July 2020]

Nicolaides KH. 2011. Screening for fetal aneuploidies at 11 to 13 weeks. Prenat Diagn 31(i):7-15

Nicolaides KH, Wright D, Poon LC, et al. 2013. First-trimester contingent screening for trisomy 21 by biomarkers and maternal blood cell-free DNA testing. J Ultrasound Obstetrics Gynecol 42(one):41-50

PHE. 2018. Down's, Edwards' and Patau'south syndromes screening. Handbook for laboratories. Public Health England, NHS Fetal Anomaly Screening Programme. world wide web.gov.uk [Accessed Feb 2020]

PHE. 2020. Screening tests for you and your baby. Public Health England. www.gov.u.k. [Accessed Feb 2020]

RANZCOG. 2018. Prenatal screening and diagnosis of chromosomal and genetic conditions in the fetus in pregnancy. Royal Australian and New Zealand College of Obstetricians and Gynaecologists, Clinical guideline, C-Obs 59. world wide web.ranzcog.edu.au [Accessed February 2020]

Great britain NSC. 2016. The Britain NSC recommendation on Downwards's syndrome screening in pregnancy. United kingdom National Screening Commission. legacyscreening.phe.org.uk [Accessed Feb 2020]

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Source: https://www.babycenter.com.au/a544491/nuchal-translucency-nt-scan

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