What Is A Nuchal Translucency Scan?
A nuchal translucency (NT) scan, also known as the nuchal translucency ultrasound or NT ultrasound, is a prenatal screening test performed during the first trimester of pregnancy. The scan involves measuring the thickness of the nuchal translucency, which is a small fluid-filled space at the back of the fetus’s neck. The primary purpose of the nuchal translucency scan is to assess the risk of certain chromosomal abnormalities, particularly Down syndrome (trisomy 21) and other genetic conditions such as trisomy 18 and trisomy 13. The thickness of the nuchal translucency is used as an indicator because an increased thickness may indicate an increased risk of these conditions.
The scan is usually performed between 11 and 14 weeks of gestation. During the procedure, an ultrasound machine is used to obtain an image of the fetus, and the sonographer or specialist measures the thickness of the nuchal translucency using specific guidelines. In addition to the measurement, other factors like the mother’s age, blood tests, and the exact gestational age are taken into account to calculate a combined risk assessment.
It’s important to note that the nuchal translucency scan is a screening test and not a diagnostic test. If the results indicate a higher risk, further diagnostic tests such as chorionic villus sampling (CVS) or amniocentesis may be recommended to confirm or rule out any chromosomal abnormalities.
The scan itself is non-invasive and generally safe for both the mother and the fetus. It provides valuable information to expectant parents about the potential risk of certain genetic conditions, allowing them to make informed decisions about further testing or to prepare emotionally and medically for the potential outcomes.
Preparation For A Nuchal Translucency Scan?
There is very little preparation required. You should have some fluid in the bladder, but not be uncomfortably full. This is to ensure that the inside of the abdominal area is seen clearly on the ultrasound images. The radiology facility where you are having the ultrasound will provide you with information about this. It is a good idea to wear comfortable clothing that gives easy access to your lower abdominal area.
Protocol measurement Of Nuchal Translucency.
A. The gestational period must be 11 to 13 weeks and six days.
B. The fetal crown-rump length should be between 45 and 84mm.
C. The magnification of the image should be such that the fetal head and thorax occupy the whole screen.
D. A mid-sagittal view of the face should be obtained. This is defined by the presence of the echogenic tip of the nose and rectangular shape of the palate anteriorly, the translucent diencephalon in the Centre and the nuchal membrane posteriorly. Minor deviations from the exact midline plane would cause non-visualization of the tip of the nose and visibility of the maxilla.
E. The fetus should be in a neutral position, with the head in line with the spine. When the fetal neck is hyperextended the measurement can be falsely increased and when the neck is flexed, the measurement can be falsely decreased.
F. Care must be taken to distinguish between fetal skin and amnion.
G. The widest part of translucency must always be measured.
H. Measurements should be taken with the inner border of the horizontal line of the callipers placed ON the line that defines the nuchal translucency thickness – the crossbar of the calliper should be such that it is hardly visible as it merges with the white line of the border, not in the nuchal fluid.
I. In magnifying the image (pre or post freeze zoom) it is important to turn the gain down. This avoids the mistake of placing the calliper on the fuzzy edge of the line which causes an underestimate of the nuchal measurement.
J. During the scan more than one measurement must be taken and the maximum one that meets all the above criteria should be recorded in the database.
K. The umbilical cord may be round the fetal neck in about 5% of cases and this finding may produce a falsely increased NT. In such cases, the measurements of NT above and below the cord are different and, in the calculation of risk, it is more appropriate to use the average of the two measurements.
What Happens if an NT Scan Is Abnormal?
If an NT scan is found to be abnormal, it suggests an increased likelihood of a chromosomal abnormality, but it does not provide a definitive diagnosis. A few potential outcomes may occur:
A. Further testing:- An abnormal NT scan result may prompt your healthcare provider to recommend additional diagnostic tests to confirm or rule out the presence of a chromosomal abnormality. These tests can include chorionic villus sampling (CVS) or amniocentesis, which analyze the baby’s genetic material directly.
B. Combined screening:- The NT scan is often part of a combined screening test that includes additional blood tests. The blood tests measure specific substances in the mother’s blood to provide more information about the risk of chromosomal abnormalities. If the combined screening results indicate a higher risk, further testing may be advised.
C. Counseling and support:- Receiving news of an abnormal NT scan can be distressing for expectant parents. Your healthcare provider should provide you with appropriate counseling and support, explaining the implications of the abnormal result and discussing the available options. Genetic counselors can offer additional guidance and help you make informed decisions.
D. Monitoring and follow-up:- Depending on the specific circumstances and the severity of the abnormality, your healthcare provider may recommend more frequent ultrasounds, additional screenings, or specialized consultations with fetal medicine specialists. These measures aim to monitor the development of the baby more closely and provide timely intervention if necessary.
FAQs.
Q. What is nuchal translucency scan for?
nuchal translucency scan done for Down syndrome and other genetic problems in the baby.
Q. What week is best for nuchal translucency?
The accuracy is highest when the lab work is done between 10 and 11 weeks into the pregnancy, and we recommend scheduling the nuchal scan between 12 and 13 weeks.
Q. What is normal nuchal translucency scan?
An NT of less than 3.5mm is considered normal when your baby measures between 45mm and 84mm from crown to rump
Q. Can we identify gender in NT scan?
This test can now also tell you the gender of the fetus (this is 95% accurate).
Q. Is nuchal translucency test necessary?
A nuchal translucency screen is recommended for all pregnant women and is often one of several routine prenatal screenings during the first trimester.
Q. What is normal range for nuchal translucency at 12 weeks?
Normal screening NT measurement at 12 weeks to be under 3.0 mm.
Q. What if nuchal translucency is high?
An increased NT has also been associated with a high risk of miscarriage or fetal death.
Q. Is NT 1.2 mm normal at 12 weeks?
Nuchal translucency measured at 12 weeks 5 days 1.2mm is within normal limits.
Q. Is 2.5 nuchal translucency normal?
A very small nuchal translucency measurement – less than 2.5 mm – places the pregnancy in a low-risk group for problems, such as fetal heart abnormalities.
Q. Which week is best for NT scan?
When is a nuchal translucency scan done? A nuchal translucency scan is done between 11 and 14 weeks of pregnancy.
Q. Which baby position is not proper for NT scan?
The fetus should be in a neutral position, with the head in line with the spine.
Q. What is the actual size of 13 weeks pregnant?
Your baby measures about 7.5 cm from head to bottom and weighs about 30 gm.
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