NT Scan
Nuchal translucency scan is part of the ultrasound that most pregnant women have around 12 weeks of pregnancy. If you want to have the scan, the health professional performing the ultrasound will measure your baby's nuchal translucency (a fluid-filled space at the back of your baby's neck).
NT scan is a screening test that is done during the first trimester of pregnancy. It is not uncommon to have fluid or clear space at the back of your neck for a fetus. However, too much open space may mean Down syndrome, or other chromosome defects may be seen such as Patau syndrome or Edwards syndrome.
Purpose of an NT scan
Whether your baby has a high or low risk of a chromosomal abnormality, the results of a nuchal translucency scan can tell you. Our cells in the body have several elements, including a nucleus. Our genetic material is retained by the nucleus. In most instances, there are 23 pairs of chromosomes in the nucleus, which are inherited equally from both parents. There is an extra copy of chromosome 21 in people born with Down syndrome. If the baby has down syndrome which cannot be cured, causes developmental delays and distinct physical features. These include:
- A small stature
- Eyes which have upward slant
- Low muscular tone
It is a genetic disorder that is very common. Patau syndrome and Edwards syndrome are unusual effects that are often fatal. Unfortunately, during the first year of life, most babies born with these abnormalities die.
When is an NT scan scheduled during pregnancy?
The transparent space in the back of a developing baby’s neck can disappear by week 15, so an NT scan should be done in the first trimester.
By week 15, the clear space in the back of a developing baby's neck will disappear, so in the first trimester, an NT scan should be completed. This test will also require blood work to measure the plasma protein levels and, human chorionic gonadotropin (HCG), a maternal hormone. Abnormal levels of either can indicate a problem with chromosomes.
How does an NT scan work?
Your doctor or technician will have an abdominal ultrasound done during the screening. Alternatively, you may get a transvaginal examination, where you put an ultrasound probe into your vagina.
To produce an image from inside the body, an ultrasound uses high frequency sound waves. The translucency, or clear space, at the back of your baby's neck is measured by your doctor or technician from this image. They will then input your age or birth date, in a computer program to measure the probability of your baby having an abnormality.
Down syndrome or any other chromosome abnormality cannot be diagnosed by NT scan. The scan only predicts the risk. Speak to your doctor about the blood tests that are available. We can also help decide your baby's risk.
The accuracy rate varies, as with any prediction. The screening is approximately 85 percent effective for assessing the likelihood of Down syndrome if you combine an NT scan with blood testing. The accuracy rate drops to 75 percent if you do not combine blood testing with the scan.
How to prepare for your test
An NT scan requires no special preperation. Testing is done in about 30 minutes in most cases. You'll lie down on an examination table during the scan while the technician moves an ultrasound wand over your stomach.
If you have a full bladder, the ultrasound pictures will be easier to interpret, so your doctor will suggest drinking water around one hour before your appointment. Ultrasound equipment requires access to the lower abdomen, so make sure you wear comfortable, open clothing.
Scanning results will be available on the same day as the exam, and your doctor may speak to you about the results before you leave. It is necessary to note that it does not necessarily mean that your baby has a chromosome issue if you obtain an irregular result from an NT scan. Similarly, normal test results do not guarantee that your baby with Down syndrome will not be born.
This test isn't perfect. There is a false-positive rate of 5 percent. In other words, positive results are given to 5% of women tested, but the baby is healthy. Your doctor may recommend another blood test after a positive result, called prenatal cell-free DNA screening. To measure your baby's risk for Down syndrome and other chromosome abnormalities, this test tests fetal DNA in your bloodstream.
Results
An NT scan provides an estimate of the likelihood of such issues for your baby; it does not provide a diagnosis. You may decide to have chorionic villus sampling (CVS) or amniocentesis based on the information from the NT scan, which can provide a diagnosis. CVS and amniocentesis are invasive tests that bear risks, including an increased risk of miscarriage, but they are typically healthy.
Your Choice
This first trimester screening test should be given to all pregnant women, but this is not compulsory. If you do want to have a nuchal scan, that is harmless for mother and baby, consult with your doctor.