THE NUCHAL TRANSLUCENCY SCREENING (NT Scan)
The nuchal translucency (NT) screening is a prenatal test that assesses the risk of certain chromosomal abnormalities in a developing fetus, particularly Down syndrome (trisomy 21) and other conditions such as trisomy 18 and trisomy 13. This screening is typically performed during the first trimester of pregnancy, usually between weeks 11 and 14.
The test involves measuring the thickness of a fluid-filled space at the back of the fetal neck. This space is known as the nuchal translucency. Abnormalities in the nuchal translucency measurement can be associated with an increased risk of chromosomal abnormalities, as well as other genetic disorders and certain congenital heart defects. At the time of the NT ultrasound, other basic anatomical structures of the Baby can also be assessed. If an anomaly is noted, this may also indicate increased risk of a genetic or structural condition.
Here's how the process generally works:
Ultrasound: During the NT screening, a specialized ultrasound is performed to measure the nuchal translucency. The ultrasound technician will measure the thickness of the fluid-filled space at the back of the fetal neck.
Blood Test: In addition to the ultrasound, a blood test is often done to measure specific hormones and proteins in the mother's blood, such as pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG). The combination of the ultrasound measurement and the blood test results helps provide a more accurate assessment of the risk.
Risk Assessment: The nuchal translucency measurement, combined with the results of the blood test and factors such as the mother's age and gestational age, is used to calculate a risk score for certain chromosomal abnormalities. This risk score indicates the likelihood that the fetus has a chromosomal abnormality.
Further Testing: If the calculated risk is found to be higher than a certain threshold, further testing, such as chorionic villus sampling (CVS) or amniocentesis, may be recommended to confirm or rule out the presence of a chromosomal abnormality.
It's important to note that the nuchal translucency screening is a screening test, not a diagnostic test. This means that it provides an estimate of the risk but does not provide a definitive diagnosis. If the screening indicates an increased risk, additional testing is usually recommended to confirm whether the fetus has a chromosomal abnormality.
The decision to undergo the nuchal translucency screening, as well as any subsequent testing, should be based on discussions with your healthcare provider. They can provide information about the benefits, limitations, and potential risks of the screening, as well as help you make an informed decision based on your individual circumstances.
Sources: American College of Obstetricians and Gynecologists (ACOG), NIH
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