Beginning in the mid-nineties, doctors and sonographers began implementing a new type of prenatal screening. The name of this new screening tool: the Nuchal Translucency Screening or NT screening. Performed in the first trimester via ultrasound, usually in conjunction with a maternal blood test, the Nuchal translucency screening evaluates the chances of a fetus having a genetic disorder or heart defect.
What is the Nuchal Translucency Screening?
The NT screening is a painless, non-invasive procedure that measures the amount of fluid present behind a fetus’s neck. Fetuses with genetic abnormalities will have a larger collection of fluid in this area. It’s important to keep in mind that this screening tool is not meant as a diagnosis. Results from this screen assist doctors in determining what, if any, further testing may be needed to make a diagnosis.
When is the Nuchal Translucency Screening performed?
A NT screening is typically performed between 11 and 13 weeks gestation. This time period is critical for best results, as the fetus’s neck is still transparent at this point. Testing too soon or too late will give inaccurate results.
Who should have the Nuchal Translucency Screening?
Any pregnant woman can have a NT screening performed. Some women, especially older moms to be and women with histories of genetic abnormalities are encouraged to have the screening performed. Again, the NT screening is not used to diagnose a problem; it is used to assist doctors in making further suggestions for treatment, if needed.
What do the results of the NT screening mean?
As previously stated, the NT screening is typically performed in conjunction with a maternal blood test. A small sample of blood is taken from the woman and tested for specific markers that only occur during pregnancy. The results from the blood tests return either “Screen Negative” or “Screen Positive”. A Screen Positive means the woman is in a high risk group for carrying a child with Down syndrome, Trisomy 18 or Trisomy 13. A Screen Negative means the woman is in a lower risk group for carrying a child with Down syndrome, Trisomy 18 or Trisomy 13.
It is important to realize that, much like the NT screening results, one can not assume, based on the results of the blood testing, that they are carrying a child with a genetic abnormality or they are not. The blood tests are just another tool to help evaluate the likelihood that the fetus has a genetic abnormality. The accuracy of the NT screen also depends on the skill of a sonographer.
The only way to know for certain whether a fetus has a genetic abnormality is by having a CVS or Amniocentesis performed. Both tests are considered invasive and come with the risk, although slight, of miscarriage. Results from both the blood testing and NT Screen help doctor’s decide what should happen next.
Some women choose to decline the NT screening and the blood tests. Some women choose to have the screening performed so that they prepare in case they are having a child with special needs. Each choice is a valid and personal one.
Unlike a CVS or Amniocentesis, there are no risks involved with having a NT screen performed. Any questions or concerns should be directed to your health care provider.