Nuchal Translucency Non-Invasive Prenatal Testing

There are a variety on non-invasive prenatal tests that you can have during your first trimester. In addition to blood tests, that screen for chromosomal abnormalities, you can have a nuchal translucency screening to further look for, and possibly detect, possible health conditions of your baby. While the nuchal translucency test will not definitively determine a congenital abnormality, it can help you to gauge the risk and see if you should consider additional testing, such as an amniocentesis. 

During the first trimester, the area at the back of a baby’s neck is transparent. At 14 weeks, the area stops being transparent, making the test unreliable. Therefore, if your prenatal blood work, that will be done around 9 weeks, shows any signs of a possible chromosomal abnormality, it is important to discuss with your doctor whether a nuchal translucency test is worth having. 

Some doctors automatically have this area of the body screened during the initial ultrasound, regardless. Ask him if this scan is part of your ultrasound if you are unsure.  

Doctor’s start with standard blood tests that screen for down syndrome (trisomy 21), trisomy 18, and trisomy 13. They also screen for congenital heart defects. It is not uncommon for woman carrying health babies to have false-positives with these tests; however, it is important to conduct further non-invasion tests to rule out a disorder.  

If your blood tests show elevated levels of cell-free DNA, or DNA markers from the baby, an ultrasound is typically ordered to look at the space at the back of your baby’s neck. This space is an important place to look as a trained technician can measure the amount of fluid that is accumulated.  

In babies with a chromosomal abnormality, such as downs syndrome, there is typically a higher level of fluid in this area, making the translucent space larger.

If you have a nuchal translucency test, and there is a higher level of fluid at the back of the baby’s neck, he could have Downs Syndrome. 

Aside from the back of the neck, the fetal nasal bone is also looked at during an ultrasound. If no nasal bone is seen, this is also an indication of chromosomal abnormalities. As with the nuchal translucency exam, the fetal nasal bone screening is not a definitive diagnosis of downs syndrome or another chromosomal abnormality, however, it is a good way to identify a high-risk pregnancy, which increases the odds of the baby having a birth defect.

The fetal nasal bone also needs to be looked for at the appropriate times. In an ultrasound conducted around 11 weeks, the nasal bone is almost always absent. This should not be mistaken for a birth defect, but rather normal fetal development. Rather, this screening method should be conducted between 11 weeks and 13 weeks and 6 days.

After 14 weeks the length of the nasal bone changes very little and is not as reliable a gauge for chromosomal testing as it is at the end of the first trimester.

Other Reasons
for a Sonogram

Aside from looking for the likelihood of chromosomal abnormalities, the age of the baby can also be determined using the nuchal translucency test. If the test is done after 13 weeks and 6 days, the space at the back of the neck in no longer translucent, which means the baby is in its 14th week of development, or later.