What is NT Scan, its Procedure & How it is Done?

Nuchal translucency or NT scan helps determine a baby's risk of developing congenital conditions, such as Down syndrome. Its accuracy is high when performed along with other screenings at first-trimester.

However, it is necessary to understand that the Nuchal translucency test does not diagnose a condition. It rather helps doctors assume the possible risks of a genetic or chromosomal condition based on how the fluid behind a baby’s neck appears. More fluid may result in the mentioned conditions.

Nuchal translucency is an ultrasound that measures the fluid present behind a baby's neck in the first trimester of pregnancy. Test reports are normal when a small amount of fluid is present behind the baby's neck. Conversely, when the fluid amount is high, it suggests the baby is at a heightened risk of developing a genetic or chromosomal variant.

The purpose of nuchal translucency is to determine whether a baby has developed with a normal nucleus containing 23 chromosomes inherited equally from both parents. The test otherwise suggests- a baby developing with an extra copy of chromosome 21 develops Down syndrome.

A healthcare professional performs an NT scan procedure when a baby is between 45 to 84 millimetres from its head to its torso or 11 to 13 weeks of gestation. The test is performed at this stage, given that the fluid behind a baby's neck has a tendency to get reabsorbed after 14 weeks of gestation.

Nuchal translucency ultrasound can be done through a mother’s vagina or abdomen.

• The sonographer chooses a method based on multiple considerations, including how long a person has been pregnant and her body shape.
• If the scan is performed trans-abdominal, the person must have a few cups of water before she arrives for screening so that the bladder is full of fluid. This is done to ensure the view of the uterus is clear.
• A sonographer applies a certain type of gel on the abdomen and gently moves ultrasound probes all over the abdomen. This process is painless. 

However, when the scan is performed trans-vaginally, it takes the sonographer to drive the probe internally in a gentle manner. This may cause some discomfort, and usually is not painful. In addition, this process gives better and clearer pictures as the probe is closer to the uterus.

Nuchal translucency is measured in the sagittal plane at its maximal thickness. Therefore, the nuchal translucency measurement may have multiple ways of expression. One way is- reporting the difference in millimetres between the normal median for the CRL (Crown-Rump length) and the measured nuchal translucency.

Screening performed via NT scan is known to be 85% accurate for predicting risks of trisomy 21 and other conditions. However, it is crucial to have tests done beforehand to understand possible risks, seek treatment at the earliest, and be aware and prepared to determine how to bring up a baby with chromosomal conditions.