What Is An NT Scan? Why is it important to perform it between the 11th and 14th Week of Pregnancy?
Discovering that you are pregnant gives rise to a myriad of emotions in you. You may feel intense joy at some moment, while at the other you may feel stressed, anxious or fearful of your baby’s health. You have very little control over your emotions, but you can’t take your baby’s health for granted. So you need to follow up with your doctor from time to time to monitor your and your’s unborn child’s health. Your doctor may recommend specific tests to check if you or your child is affected with a particular health condition.
Some of these tests are in the form of screenings, and these help doctors determine the amount of risk you or your child may have for a specific disease. Screenings can help to identify problems like anemia or gestational diabetes in women. Whereas in unborn children, these can help to detect the presence of chromosomal abnormalities.
The results obtained from these screenings can be positive or negative. A positive result does not ascertain that the child has a chromosomal abnormality. Similarly, a negative result does not guarantee that the unborn child does not have a chromosomal abnormality. Additional diagnostic tests like chorionic villus sampling or amniocentesis must be performed to confirm whether the child has a chromosomal abnormality or not.
What is an NT Scan?
NT Scan, also known as the nuchal translucency test, is a screening test. Non-invasive in nature, it is performed to check the extent of risk (high or low) your child carries for a particular chromosomal abnormality.
NT scan is primarily used for assessing the risk for Down Syndrome and other chromosomal abnormalities like Edwards Syndrome and Patau Syndrome. Also, it helps to determine the risk for some structural problems like major congenital heart problems, abdominal wall and skeletal defects.
Babies born with Down syndrome contain an additional copy of chromosome 21, and this syndrome is incurable and causes developmental delays in them. Such babies have distinct physical characteristics like a small stature, eyes with an upward slant and a low muscle tone.
Edwards syndrome and Patau syndrome are rare chromosomal abnormalities and often prove fatal for babies. Unfortunately, most babies born with these abnormalities die within the first year of their life.
Ultrasounds use high-frequency sound waves to create an image from inside the patient’s body. The nuchal translucency test also uses ultrasound to assess the risk for a medical condition.
All pregnant women are offered the NT scan along with a blood test as a part of first-trimester screening options. The first trimester starts on the first day of the last period and lasts till the end of the 13th week. Apart from the first trimester, screenings are also done in the second and third trimesters.
In an NT scan, a doctor or technician measures the clear (translucent) space in the tissue at the baby’s neck. This translucent space is the nuchal translucency. During the first trimester, babies having abnormalities tend to accumulate more fluid at the back of their neck, and as a result, this clear space becomes larger than average.
Apart from nuchal translucency, some doctors also look for the presence of the fetal nasal bone during the NT scan. If no nasal bone is visible in the developing baby, some experts believe this increases the chance of chromosomal abnormalities in the baby.
What is the right time for performing the NT Scan?
The NT scan must be conducted when a woman is between 11 and 14 weeks pregnant, and this is when the base of her baby’s neck is still transparent. The last day for doing this scan is when a woman is 13 weeks and six days pregnant.
How is the nuchal translucency test performed?
An NT scan requires no special preparation. In most cases, the scan gets completed in just 30 minutes. The doctor will recommend you drink water an hour before the procedure as ultrasound pictures are easier to read with a full bladder. The doctor will ask you to lie down on an exam table to perform the scan. After which, the sonographer will move an ultrasound wand over your stomach. Correspondingly, the pictures of the baby will become visible on the monitor.
The sonographer first confirms the baby’s gestational age by measuring him from crown to rump to see if his size fits the babies of his age. Then he positions the transducer (a sensor) over the abdomen. It shows the baby’s nuchal translucency on the monitor, and the sonographer uses calipers to measure its thickness on the screen.
You can get the results of the nuchal translucency test right away or you may have to wait for ten days if the doctor needs to send the data to a processing center.
How to Interpret NT Scan Results?
The doctor will use a computer program to calculate the amount of risk your growing child carries for a chromosomal abnormality. He will enter your age or date of birth in the program, and it will accordingly give the results.
The results will be in the form of a ratio that expresses the chances of your baby having a chromosomal defect. You will find it confusing to interpret the results yourself. So you are advised to talk to your doctor or a genetic counselor to grasp a better understanding of the results.
The doctor may also tell you that your results are normal or abnormal for a specific condition, depending on whether the ratio is below or above a particular cutoff.
A normal screening result (screen negative) does not guarantee that your child does not have a chromosomal abnormality. But it does suggest that the occurrence of a chromosomal problem is unlikely. Similarly, an abnormal screening result (screen positive) does not mean your baby carries a chromosomal problem, and it just indicates that your baby is more likely to have a problem. The majority of screen-positive babies don’t have a problem. Only one-third of babies with an increased translucency measurement are born with chromosomal defects.
What do doctors consider for calculating NT scan results?
Nuchal translucency measurement is not the sole factor that doctors consider for determining the result of the NT scan. They also consider other factors like the mother’s age, the baby’s gestational age, and the blood test results.
Although chromosomal abnormality can occur in the baby of any mother, the risk of its occurrence increases with the increased age of the mother. For example, if your age is 25 years, your baby’s risk of having Down Syndrome is 1 in 1,200, but if your age is 40 years, this risk increases to 1 in 100. Because of this, doctors consider mother’s age as one of the factors in determining NT scan results.
Is the Nuchal Translucency test accurate?
Like other screening tests, the nuchal translucency test is also not perfect, and it cannot detect all cases of Down Syndrome. The NT test provides both false-negative results and false-positive results.
A false-negative result identifies your baby as a low risk for Down Syndrome while he has this chromosomal condition.
A false-positive result suggests that your child is at increased risk for Down Syndrome or other conditions, but he has no problem.
What to do if your nuchal translucency test result indicates a problem?
After talking with your practitioner or genetic counselor, you can better understand whether your child is at an increased risk for a chromosomal condition.
If there is an increased risk, the next step is to get a diagnostic test like amniocentesis or CVS conducted. The diagnostic test is necessary to confirm a positive screening result for your baby and to obtain a definitive diagnosis.
A needle is inserted through the stomach into the amniotic sac to retrieve a fluid sample for the amniocentesis diagnostic test. Amniotic fluid contains cells that provide genetic information about the baby.
In CVS or chorionic villus sampling, a mother’s placental tissue sample is removed and tested for chromosomal abnormalities and genetic problems.
These diagnostic tests are more invasive and carry a small risk of miscarriage.
Suppose you decide against diagnostic testing. Then you can opt for NIPT, quad screen and detailed ultrasound to know more about your baby’s health and development. The NIPT is a blood test available to all pregnant women at the beginning of 10 weeks of pregnancy. The quad screen is a blood test performed in the second trimester, whereas a detailed ultrasound is performed in 18 to 20 weeks.
A detailed ultrasound can help detect soft markers of chromosomal disorders. Some of these markers are a bright bowel, a bright dot in the heart, short limbs and specific problems in the kidneys. This ultrasound can also be used for finding anatomical defects like spina bifida.
Is it mandatory to undergo the NT scan and diagnostic tests?
It is your discretion to go for the nuchal translucency scan or any diagnostic tests or ignore them altogether. You may choose one, two, or more tests out of all the tests offered to you during the pregnancy and avoid the rest.
By now, you may have understood the need to get the NT scan conducted on your growing baby. If you are keen to get this scan done in Livermore, California, DigiBaby is the place to go. We also provide this facility in Woodridge, Illinois and Mesa, Arizona. Our medical center is equipped with state-of-the-art pregnancy screening, diagnostic equipment, and expert medical professionals to provide you with a safe and satisfying medical experience during your pregnancy. Thus, making your journey to motherhood smooth and enjoyable.