The first trimester is an important phase of pregnancy, accommodating pregnancy scans and the first-trimester ultrasound scan. NT scan or Nuchal Translucency scan is also a part of the first-trimester scan, involving NT measurements done with the help of ultrasound waves.
Scans during pregnancy help identify the growth and development of the foetus. An NT scan measures the foetal nuchal translucency- the fluid space at the back of the baby’s neck. This scan can help rule out the baby’s risk of developing chromosomal abnormalities like trisomy 21, trisomy 13, or trisomy 18.
This prenatal scan can reassure if the baby is developing normally or with any genetic abnormalities. This article discusses everything you need to know about the first trimester NT scan.
What is an NT scan in pregnancy?
A nuchal translucency or an NT Scan is a typical first-trimester ultrasound scan that determines the measurement of nuchal translucency (NT). Nuchal translucency (NT) is the fluid typical at the back of the baby’s neck. The NT measurements help determine the risk of the foetus having a chromosomal anomaly, including Down syndrome (trisomy21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13).
Why do you need an NT scan in pregnancy?
The probability of having a child with abnormalities is high in older couples. However, NT scans are optional screening tests offered in the first trimester to every couple.
As aforesaid, the NT scan looks for the fluid-filled space at the back of the baby’s neck, also referred to as the nuchal fold. The more fluid build-up at the back of the baby’s neck, the more will be the chances of the baby developing a chromosomal condition.
Excess nuchal fold measurement can indicate conditions, such as:
Apart from these conditions, excess fluid can also significantly increase the risk of congenital heart conditions in the baby. NT Scan is a screening test that can help screen the likelihood of anatomical defects in the unborn that can develop genetic or structural anomalies in the baby in the future.
During the NT scan, the doctor can also determine other criteria, such as
- Ectopic pregnancy,
- Check the baby’s heart rate,
- Presence of multiple pregnancies.
When is the NT scan done?
The doctor may recommend an NT scan, usually between 11 to 13 weeks of gestation or when the baby’s CRL (crown to rump length) is between 45 mm to 84 mm.
The NT fluid is optimally seen during this time as the fluid can get reabsorbed after 14 weeks of gestation. And cannot be measured in later pregnancy. Hence, NT scans are typically a part of first-trimester scans.
How is an NT scan done?
A specialised technician trained in sonography or a radiologist conducts the NT scan in a radiological setup. The NT scan can be done in either of the following ways.
- Transabdominally- along the abdomen, or
- Transvaginally- through the vaginal opening.
If the scan is done transabdominally, the doctor will advise you to keep your bladder full by drinking more water. This allows the radiologist to visualise the inside of the abdomen more easily and clearly. During the transabdominal NT scan, the radiologist will apply the gel for smooth movement of the ultrasound probe and gently move the probe to help create images of the growing foetus.
In the case of a transvaginal NT scan, the probe is lubricated and gently passed into the vagina. You may experience slight discomfort or pain while the probe gets inserted into the vagina. Transvaginal scans can give a clear or detailed image of the foetus as the probe gets closer to the uterus.
However, both types of NT scans are safe and effective and do not harm the mother or the baby, nor do they increase the risk of pregnancy loss.
What do the results of an NT scan indicate?
As mentioned earlier, the NT scans help calculate the baby’s risk of developing a congenital deformity. Blood tests generally accompany NT scans, and the combined finding of the blood test and scans can give a more accurate screening outcome. The NT scan combined with blood tests is a “combined-first trimester screening.”
Along with The NT measurement, NB or nasal bone presence is also checked during the scan, which helps detect the risk of chromosomal abnormality.
The normal level of NT measure indicates the lower chances of a genetic condition in the foetus. Higher than normal NT measure means that there is a chance of the baby having a genetic or congenital abnormality.
However, NT scans are basic screening tests and must be followed by confirmatory diagnostic tests to confirm the presence of possible genetic conditions (if any).
Though the NT fluid measurement increases during the 11 to 14 weeks of gestation, the NT fluid levels need to be optimum during this period, after which the excess NT fluid gets reabsorbed. The normal NT measurements at 11 weeks must be 1-2.8 mm, and by 14 weeks, it can increase to 3 mm.
The NT measurements above 3 millimetres (avg) may require genetic counselling and additional testing. A genetic counsellor will discuss additional diagnostic testing options, like chorionic villus sampling (CVS) or amniocentesis after an elevated NT measure.
The NT scan results are generally reported as ‘low-risk’ and ‘high risk’.
- Low risk- means that the risk of the baby having a chromosomal abnormality is less than 1 in 300.
- High risk- means that the risk of the baby having the abnormality is higher than 1 in 300.
The high-risk NT screening and blood test result may require you to have an invasive diagnostic confirmation through CVS or amniocentesis.
Sometimes, couples choose direct diagnostic tests- CVS or amniocentesis for more definitive or accurate information about the baby’s condition.
Frequently Asked Questions
How accurate is an NT scan in pregnancy?
According to statistics, Nt scans help detect 70% of trisomy cases, including trisomy 21, trisomy 18, and trisomy 13. However, NT scans combined with blood tests can increase the accuracy to 95% in predicting possible chromosomal conditions in the foetus.
Are there any risks associated with an NT scan?
NT scans are safe and low-risk scans that are non-invasive.
What is the turnover period for an NT scan?
NT scan is an ultrasound screening that provides results immediately. However, combined first-trimester screening- including a blood test, may take a week to calculate the combined or overall risk of the unborn.
Conclusion
A nuchal translucency or NT scan is a non-invasive first-trimester screening that can help detect the likelihood of the baby having a congenital condition. The NT scan is ideally done between 11-14 weeks of gestation.
And abnormal NT scan results need to be followed by additional diagnostic invasive tests to rule out the possible genetic condition in the unborn.
Your doctor or a genetic counsellor can take you through these tests and help you sail through a healthy pregnancy while preventing the possibility of chromosomal abnormalities in the unborn baby.
