The nuchal translucency ultrasound, also known as the NT or NTS, is one of the many tests you might have during your pregnancy.
This test is offered to all pregnant women, in conjunction with a blood test.
For some women, this type of investigation causes a little anxiety – especially if they don’t know what it is or what is required.
Here are answers to 11 common questions, to give you more information and settle any concerns you have about the nuchal translucency scan.
#1: What is nuchal translucency screening?
Nuchal translucency screening helps doctors to identify your baby’s risk for certain chromosomal disorders.
The NT assesses the risk of chromosomal abnormalities such as Trisomy 21 (Down syndrome), Trisomy 13 (Patau Syndrome), and Trisomy 18.
There are two steps involved in this screening:
- Blood test. This looks for levels of pregnancy associated plasma protein-A (PAPP A) and human chorionic gonadotropin (hCG)
- Ultrasound scan. This looks at a specific areas of the developing baby for signs that might indicate abnormalities.
The mother’s age is also taken into consideration when looking at the data from the nuchal translucency screening.
For more information on the nuchal scan please read 9 Procedures You Might Want To Reject During Pregnancy.
#2: Do I have to have the nuchal translucency test?
It’s important all expecting mothers are aware the nuchal translucency test is recommended but not compulsory.
Some women could be at higher risk for having a baby with chromosomal abnormalities and it is their personal decision whether or not to have the screening done.
Other women will choose not to have the test, especially if the outcome will have no impact on their decision to continue with the pregnancy.
#3: Should I have a nuchal translucency scan?
It is a personal decision whether to have the NT scan or not.
Factor that increase the risk of having a baby with a chromosomal disorder are:
- Maternal age over 35 years
- Family history of certain chromosomal disorders
- Previous pregnancy affected by chromosomal abnormalities.
If you decide to go ahead with the nuchal translucency scan and have concerns about the results, talk to your doctor or midwife about how the results might affect you.
Here are answers to 11 common questions you might have about the nuchal translucency scan:
#4: What do they look for in a nuchal translucency scan?
The scan is an ultrasound that will look at your baby’s body to assess whether there are any identifiable signs of chromosomal abnormalities.
The health practitioner doing the ultrasound will measure your baby’s nuchal translucency.
The nuchal translucency is the fluid-filled space at the back of your baby’s neck (the nuchal fold).
Babies who are developing normally have fluid under the skin. Excess amounts of fluid, however, indicate the possibility of chromosomal disorders.
The fluid is measured and assessed, along with the data from your blood test.
#5: What can I expect at a nuchal translucency ultrasound?
If you’ve decided to go ahead with having the scan, the NT requires a referral from your doctor or midwife.
When you book your scan, you’ll be given a few instructions.
You should have a full bladder before arriving. This makes it easier for the sonographer to get images of your baby, as your bladder pushes the uterus up and out of the lower pelvis.
You’ll also need to wear clothes that allow easy access to your belly. Some clinics will offer you a gown to wear.
The sonographer will put some ultrasound gel on your abdomen, run the ultrasound probe or wand over your tummy to locate your baby in your uterus, and take some images.
Measurements will be taken, and the NT measurement calculated. It will be forwarded to your doctor or midwife, along with your blood test, and you will book an appointment for your screening results.
You might be interested in reading Ultrasounds In Pregnancy – Risks and Benefits.
#6: What is a normal nuchal translucency measurement at 12 weeks?
The sonographer measures the size of the nuchal fold to see if the amount of fluid is normal or excessive.
A normal nuchal translucency will measure less than 3.5 mm when your baby measures between 45 mm and 84 mm. The NT increases in proportion to your baby’s growth, so the number of weeks gestation you are needs to be taken into account when you have your scan.
Anything under 3.5 mm is considered within the normal range, meaning the likelihood of Down syndrome is low. As the measurement of the NT increases, so does the chance of chromosomal abnormalities.
Babies with a nuchal translucency measurement of 6 mm or more have an increased chance of Down syndrome and other chromosome abnormalities, including congenital heart defects.
Remember, this measurement is taken into consideration along with blood tests and maternal age.
#7: How accurate is 12 week scan for Down syndrome?
Receiving the news you have an abnormal NT screening result in pregnancy can be very distressing.
However, you must keep in mind this result in the first trimester doesn’t mean your baby has a chromosomal abnormality. It is a risk assessment screening test, not a diagnostic tool.
On the other hand, a normal test result doesn’t guarantee your baby won’t be born with Down syndrome.
This test isn’t perfect. It’s known to have a 5% false-positive rate.
The results of the NT scan, the mother’s age, and the blood test results provide a combined risk of chromosomal abnormality, with around 85% accuracy.
You might like to read Expecting a Baby With Down Syndrome – A Mother’s Story.
#8: When should I have a nuchal translucency ultrasound?
The first-trimester screening nuchal translucency scan is combined with a blood test to assess the risk of chromosome abnormality. If you’ve decided to have the NT, your doctor or midwife will organize a referral for the ultrasound scan and a pathology request for the blood test.
It’s important these screening tests are done between 11 and 13 weeks of pregnancy to increase the accuracy rate of the results.
Make sure you are well informed before this time. If you decide to have the NT, it will be included as part of your first-trimester pregnancy scan.
Having the chromosomal abnormalities NT screening test at 12 weeks is ideal, as accuracy is best at this time.
However, if you’re more than 14 weeks, you might be offered a second-trimester maternal serum screening.
#9: Does a thick nuchal fold mean Down syndrome?
The thickened fold in the neck is only one marker used to assess Down syndrome.
A thickened nuchal fold on the back of the neck can be useful in distinguishing between a baby who has Down syndrome and one who doesn’t.
But remember, this information is taken into consideration with the results of your blood test and your age.
Even if a nuchal translucency thickness fold is seen on the baby’s neck, the risk of Down syndrome goes up by only 3%.
#10: Is the nuchal scan the same as a NIPT test?
Non-invasive prenatal testing, or NIPT, is a highly accurate blood test performed after 10 weeks of pregnancy. It looks at the fetal DNA in the mother’s blood.
NIPT is a relatively new technology that has a higher detection rate than the standard 12 week NT tests.
The accuracy of the NIPT is:
- for Down syndrome (trisomy 21), 99.5%
- for Edward syndrome (trisomy 18), 99%
- for Patau syndrome (trisomy 13), 79–92%.
NIPT is expensive but is becoming increasingly popular among pregnant women because of the high accuracy rate.
Even so, there is still a rate of false positives, which means further invasive tests will be needed if you have a positive NIPT result.
#11. What if the nuchal translucency is high?
If you have a result indicating your baby has an elevated risk of chromosomal abnormalities, it can cause a great deal of worry and stress.
Remember, this screening isn’t diagnostic, so it can’t say for certain your baby has a chromosomal abnormality.
Your doctor or midwife will offer you the options of a diagnostic test called chorionic villus sampling (CVS), or amniocentesis.
Both of these tests increase the risk of having a miscarriage, so it’s not a decision to take lightly.
Your doctor or midwife can refer you to a genetic counselor to discuss your options, so you can ask any questions and express your concerns.
A counselor will be able to explain what the tests mean and help you make an informed decision.
CVS involves a thin tube guided through the cervix, or a needle put into the uterus, to take a small piece of chorionic villus cells from the placenta. These cells contain a baby’s genetic information.
You can read more in CVS (Chorionic Villus Sampling).
Amniocentesis involves a small amount of amniotic fluid being taken from the amniotic sac around your baby.
Find out more in Amniocentesis – Definition, Risks And What To Expect.
Be aware that an abnormal result on the nuchal translucency scan doesn’t mean your baby has an abnormality. This information has a 75% accuracy rate, which means there’s still a large margin for error.
It can be stressful to be told your baby has an increased risk of chromosomal abnormalities but it’s important to seek further information and support before deciding what to do.
There is anecdotal evidence of termination of healthy pregnancies when the NT diagnosis was incorrect.