آزمایش و تصویربرداری

What is NT ultrasound?

When we talk about NT ultrasound, we refer to the nuchal translucency scan, which literally translates to the space behind the neck. This non-invasive test measures the amount of fluid accumulation behind the neck of the fetus in the first trimester of pregnancy. Accumulation of a limited amount of fluid is normal and measuring its amount helps to detect the risk of chromosomal and genetic disorders. In fact, with the help of this ultrasound, your doctor will find out if there is a danger to the fetus and if more tests are needed or not?

NT ultrasound looks at the space behind the baby's neck, which is called the nuchal fold. All babies have some fluid behind their neck; But in fetuses with genetic and chromosomal disorders, more fluid accumulates at the base of the neck.

Fluid accumulation in this area can be a sign of one of the following disorders:

• Down syndrome (extra chromosome 21)
• Pato syndrome (extra chromosome 13)
• Edwards syndrome (extra chromosome 18)
• Also, more accumulation of NT can be a sign of a double risk of congenital heart diseases.

The NT ultrasound result shows how likely these disorders are in the fetus. Also, at the same time, it displays some basic anatomical structures in the developing fetus. Other abnormalities detected in this test also increase the risk of genetic or structural disorders.

Usages of NT ultrasound

The use of NT ultrasound is the first step in measuring the risk of chromosomal disorders in the fetus. By measuring the space behind the neck and blood markers of the parents, the doctor can estimate the probability of the occurrence of disorders such as Down syndrome. Of course, keep in mind that this test is only used for screening and not for diagnosis; That is, it measures the risk but cannot confirm the diagnosis.

Read more: The Complete Guide to Anomaly Scan Pregnancy

NT Ultrasound and Gender Determination

The main purpose of NT ultrasound is not to determine gender. Of course, if during the test, the anatomy of the fetus is determined, it is in the right position and the sexual organs are visible, the sonographer may be able to determine the gender of the baby. Of course, the accuracy of this diagnosis also depends on the gestational age and the clarity of ultrasound images. If you want to know the sex of your child, it is better to do a special ultrasound to determine the gender at the appropriate gestational age.

How is the NT ultrasound performed?

In this test, the imaging specialist uses abdominal ultrasound (or in some cases vaginal ultrasound) to observe the crease behind the neck of the fetus. In the first step, the ultrasound gel is spread on the abdomen and then the manual transducer moves on the abdomen. With this, the baby's image appears on the screen and the sonographer can measure the amount of fluid that has accumulated behind the fetus's neck. The fluid environment is measured in millimeters.

The most suitable time for NT ultrasound

NT ultrasound is performed between 11 and 13 weeks of pregnancy, or when the baby is between 45 and 84 mm from the top of his head to the bottom of his body. This interval is considered the best time for NT ultrasound, because the liquid behind the neck is reabsorbed by the body until the 14th week of pregnancy. That is why NT scan is usually performed as part of screenings in the first trimester of pregnancy.

Read more: What is a congenital defect?

Who should do NT ultrasound?

In all pregnancies, there is a limited chance of There are genetic disorders in the fetus. However, this test is optional. All pregnant women can perform cervical fluid screening; Of course, as long as they are between the 11th and 13th weeks of their pregnancy.

Keep in mind that the higher the mother's age at the time of pregnancy, the higher the probability of having genetic disorders. If you are older than 35 or have a family history of genetic abnormalities, your doctor will recommend this test.

Most NT scans have normal results; But about 5% of women receive a "high-risk" result from first trimester screenings.

Receiving results and normal NT ultrasound numbers

Usually, the correlation of NT ultrasound measurements with the risk of disorders is estimated as follows:

• Less than 2 mm, less than 1% risk
• 3.4 mm, risk 7%
• Between 3.5 and 4.4 mm, 20% risk
• Between 5.5 and 6.4 mm, 50% risk
• More than 8.5 mm, 75% risk.

Also, to increase the accuracy of this screening, your doctor will also consider these enzyme markers:

• B-HCG hormone. Mother
• Alpha Fetoprotein (AFP)
• Pregnancy Plasma Protein A (PAPP-A)
• Estriol

How are NT ultrasound results interpreted?

NT ultrasound results are usually not interpreted alone. For a more accurate evaluation, the doctor examines the data of this ultrasound along with other screenings during the first trimester of pregnancy to determine the overall risk of the fetus suffering from congenital or genetic abnormalities. In most cases, at the same time as NT ultrasound, a blood test is also suggested to increase the accuracy of the screening. If the blood test is not performed, factors such as the age of the mother and the presence or absence of the nasal bone of the fetus also play a role in calculating the risk.

The doctor presents the final result in the form of a possible risk, not a definite diagnosis. For example, the result may be reported as "1 in 300 chance"; This means that out of every 300 fetuses that have such a number in the ultrasound, only one has had a congenital abnormality.

What does NT ultrasound abnormality mean?

NT screening only shows the risk of the fetus suffering from certain abnormalities, not their definite existence. If the result of this examination is abnormal, the doctor suggests additional diagnostic tests to get a more accurate answer. Among these tests, placental villi sampling (CVS) and amniocentesis can be mentioned. In the CVS method, a small amount of placental tissue is removed and examined for genetic disorders. Amniocentesis is usually performed in the later stages of pregnancy, in which, using a thin needle, some of the amniotic fluid around the fetus is removed. This fluid contains cells with genetic information that allows accurate diagnosis of genetic abnormalities or even some infections.

In some cases, the doctor may recommend a more detailed examination of the fetal heart using fetal heart echocardiography. The reason for this is that an increase in NT can be related to some fetal heart abnormalities.

Does abnormal NT mean that the fetus has Down syndrome?

No. Abnormal NT ultrasound does not mean that the fetus has Down syndrome or other congenital syndromes. This result only shows that the probability or risk of the existence of such conditions is higher than the natural state. For this reason, doctors prefer to use first trimester blood tests in addition to NT ultrasound to make a more accurate risk assessment.

How accurate is NT ultrasound?

NT ultrasound alone has limited accuracy and usually detects about 70 to 80% of fetuses with Down syndrome. For this reason, this examination is often performed in conjunction with a first trimester blood test. When NT ultrasound is combined with a blood test, the detection rate increases to about 79-90%.

Of course, these numbers do not mean that in a positive screening, the fetus has a 79-90% chance of having Down syndrome. The implication of this statistic is that among all fetuses that are truly Down syndrome, about 79 to 90 percent of them will have suspicious screening results. In contrast, about 5-21% of these fetuses may be diagnosed as low-risk on screening, which means a false negative.

false positive

On the other hand, NT ultrasound and first-trimester screening tests have about a 5% false-positive probability; That is, the screening result indicates an increased risk of an abnormality such as Down syndrome, while the fetus is actually healthy. For this reason, a positive screening result alone is not considered a diagnosis and always requires additional tests.

NT ultrasound cost

NT ultrasound cost depends on the medical center, city and your insurance coverage. Of course, if we want to look at the official imaging rates in 1404, the announced tariff is in this range:

• Insurance tariff 896,830 Tomans
• Free tariff 1,002,100 Tomans

Keep in mind that additional insurance can also cover all types of ultrasounds, including NT and anomaly ultrasounds, and reduce the cost of NT ultrasound. To use insurance, you need to do this test with a doctor's prescription.

Doctor's last word

NT ultrasound in pregnancy is a screening test, and an abnormal number only means that more investigations are needed. In many cases, even with an unfavorable outcome, the pregnancy ends in the birth of a completely healthy baby. The most important action in this situation is to talk with the attending physician about the meaning of the results and the next course of investigations. To interpret the results of this scan, you can get an instant appointment with a radiology doctor from the Dr.Doctor website and make the best decision for additional tests and continuing the pregnancy with full knowledge.

Sources:

Cleveland Clinic

babycenter

Radiopaedia

PregnancyBirthBaby

target="_blank">DRlogy

Fetal Medicine