Ultrasound scans done during prenatal tests are widely regarded as a powerful tool for detecting fetal anomalies during pregnancy. Once any abnormality is detected, investigations can be initiated, and chromosomal abnormalities can be ruled out. NT scan is one such important scan.
The NT scan, also known as the nuchal translucency test is an ultrasound scan performed to find out the unborn baby’s risk of having any chromosomal abnormalities including Down syndrome as well as congenital heart diseases. NT scan can also detect Trisomy 18 (Edward’s syndrome); Trisomy 13 (Patau syndrome); and other structural problems, such as abdominal wall and skeletal defects. NT scan is often accompanied along with a blood test. NT scan is non-invasive.
NT stands for Nuchal translucency (NT). Nuchal translucency will measure your baby’s nasal bone and the collection of fluid under the skin behind the baby’s neck. The fluid is part of baby’s normal development in the womb in early pregnancy. NT scan aims at measuring the thickness of this fluid collection. Increased levels may indicate abnormalities in the fetus.
The ultrasound pictures are easier to read if you have a full bladder, so your doctor may recommend drinking lots of water about an hour before your appointment. The ultrasound scan is usually done abdominally so it is preferable that you wear comfortable clothing that makes your lower abdomen accessible.
NT scan tests measure the size of the clear tissue, called the nuchal translucency, at the back of the unborn baby’s neck.
The duration of the scan could typically last from about half an hour to an hour depending on your baby’s neck position. If the baby’s position is not convenient the doctor might ask you to wait for a while before he/she rescans again.
The clear space in the back of a developing baby’s neck can disappear by week 15, so an NT Scan should be completed in the first trimester between 11-13+6 weeks of gestational age. Rather than the weeks of gestation it is the size of the baby that helps determine when to perform the scan. The NT scan would ideally be performed when your baby measures between 45 mm and 84 mm.
NT scan is done in the first trimester, between 11 and 14 weeks of pregnancy. This period is ideal for NT scan because during this time the base of the unborn baby’s neck is still transparent. Babies with the risk of abnormalities generally tend to gather extra fluid at the back of their neck during the first trimester; this causes the space larger than average.
The NT scan is performed by a sonographer. The clinician first confirms the baby’s gestational age, and then he positions the transducer – a sensor – over the abdomen of the expecting mother. This shows up the baby’s nuchal translucency on the monitor. The sonographer then measures the thickness of nuchal translucency on the screen with callipers. In most cases, testing is completed in about 30 minutes.
An NT scan does not require any special preparation. However, having a full bladder ensures that ultrasound pictures will be easier to read. Therefore, drink enough water about one hour before your appointment. Also, since the scan needs access to your lower abdomen, wear comfortable clothing that makes it accessible.
Results from the NT scan would be usually available on the same day. The doctor may discuss the findings with you before you leave. You will be referred to a clinical laboratory where a blood sample will be drawn to measure the levels of certain biochemical markers in your blood like Beta HCG, PAPP A (double marker test). The results of the NT Scan and the double marker test will be taken into account for a final report.
Studies have shown that an increased NT is associated with -Trisomy 21 (Down’s Syndrome) and other chromosomal conditions such as Trisomy 18 (Edward’s Syndrome) or Trisomy 13 (Patau’s Syndrome)
-Congenital heart abnormalities
-Increased risk of miscarriages
Please remember that The NT Scan is a screening test and not a diagnostic one. The test only predicts if your baby is at a high risk or low risk of having a genetic condition. As with any prediction the accuracy rate varies. If you combine the NT Scan with blood test (double marker test)the screening is about 85% accurate for predicting Down’s syndrome. If you don’t combine the blood test the accuracy rate drops to 75 %. Many women who have an abnormal first trimester screening go on to have healthy babies.
If your NT report is abnormal and your first trimester combined screening shows that you are at a high risk, then the foetal medicine specialist will counsel you regarding your options. This will include the offer of a diagnostic invasive testing to confirm the presence of a chromosomal abnormality in the baby: either a chorionic villus sampling done between 11th -14th week of pregnancy or amniocentesis which is usually carried out after the 15th week.
There are risks associated with both these procedures, including miscarriage (1%). Although this can be worrying, it is important to remember that an increased NT does not always mean there is always a health problem.
It will be up to you whether or not to have any more diagnostic tests. If the tests show there is a problem with the baby, you will be supported to make a choice that is right for you and your family.
For most women, the checks will assure that the mother and baby are doing well and no further action is required. For a small group of women, there will be an early warning signal that indicates that the doctor may need to request further tests or prescribe some medications for the remainder of the pregnancy to support the mother and the baby. By doing an assessment early in pregnancy, it enables a care pathway to be determined for you and your baby towards a happy outcome.
Trained and expert clinicians at Milann will properly guide you and help you navigate the problem. Our expert team will help you decide whether the results indicate a high enough risk that you want to have CVS or amniocentesis to get a definitive diagnosis.
An NT scan is a safe test that doesn’t cause any harm to you or your baby. Talk to an expert doctor if you experience anxiety, or are worried about how the results might affect you.