Nuchal Translucency Screening

image001 The nuchal translucency screen is a new test being done in the first trimester of pregnancy. This non-invasive ultrasound evaluation is done in combination with a blood test to check for high risk abnormalities of the chromosomes. These abnormalities can identify risk for Down Syndrome, Trisomy-21 and Trisomy 18. The nuchal translucency via ultrasound can also identify congenital defects in the heart or other areas of the fetus. However, this screening cannot identify defects in the neural tube.

This screening in the first trimester has been done in the United States for quite some time now, but has just now become a positive way to detect abnormalities of the chromosomes early in pregnancy. Early detection can assist with good prenatal care and early planning to improve quality of life for the newborn and family.

What Is the Nuchal Translucency Screening Test?

The good thing about the nuchal translucency screening test is that it is merely an ultrasound and is non-invasive. The test uses ultrasound waves to obtain measurements of the translucent space in the back of your baby’s neck. There is a clear fold of tissue and when babies have chromosomal abnormalities, there tends to be more fluid in this space in the first trimester of pregnancy. The nuchal space will appear bigger than average babies if there is a chromosomal difference.

For the test to be effective in finding abnormalities, this testing must be administered between the 11th and 14th week of pregnancy. After the 14th week, the fold in the back of the neck is no longer clear. It really must be done prior to the 13th week and 6th day. During the evaluation via ultrasound, the technician also checks for an absent or present nasal bone structure. At this time, you will have your first trimester blood work done and they will check for chromosomal problems with a test known as an alpha-fetoprotein screening. In years past, they only did the NT ultrasound if the alpha-fetoprotein came back abnormal. However, they are now doing the ultrasound as part of the routine exams in the first trimester.

The nuchal translucency ultrasound only checks for abnormalities visual to the eye and cannot completely diagnose if there is a condition. Abnormalities on ultrasound will usually be followed up by chorionic villus sampling also known as CVS and/or amniocentesis for complete diagnosis. It requires an ultrasound technician that has special training to look for these abnormalities. You may be sent to a larger hospital for your scan since this is a highly specialized test. However, most hospitals are now able to provide the screening.

The video below can give you more information on the nuchal translucency test:

Who Should I Have the Nuchal Translucency Test?

Any women who is in her first trimester of pregnancy can and should have the NT screening done. It is most important for older pregnant women over the age of 35 that carry a higher risk of chromosomal abnormalities. It is also available to women who wish to stay away from invasive testing because of the risk of miscarriage.

This test may also be done on women who have had a previous pregnancy or baby with chromosomal abnormalities. It may also be used for women who have a history of birth defects or chromosome abnormalities in their family.

If you feel you fall into the above categories for screening, talk to your doctor. The American College of Gynecologists and Obstetricians recommend the nuchal translucency screening be performed at specialized centers with ultra-sonographers that have specialized training in the test. Your doctor can help you locate a test site and order the testing for you.

How Is the Nuchal Screening Test Performed?

1. Choose a Proper Time

Between the 11th and 13th week of pregnancy in your first trimester, the doctor will order a specialized ultrasound scan. Your growing fetus needs to be between 45mm and 84 mm in size. If your baby is smaller or earlier than 11 weeks, it is too hard to see the translucent or clear fold in the back of the neck. During this time, your doctor will also order the first trimester blood screening.

If your pregnancy is later than 13 weeks and 6 days, the fluid in the nuchal fold is most likely absorbed into your baby’s lymph system and won’t be visible.

2. Take an Ultrasound

The ultrasound is painless for both you and your baby. The technician will place some gel on your stomach and use a special Doppler device to use sound waves that creates a picture. If you are overweight or have an inverted uterus, they may need to use a Doppler via your vagina. This is still painless, but may be slightly uncomfortable.

3. Measure Your Baby’s Length and the Nuchal Area

During the exam, the ultrasound technician measures the baby from the crown to rump or top of the head to the base of the spinal area. After the length is measured, they move to the nuchal area to measure how wide it is. If the timing is right, the skin in the area is white and fluid will appear black.

The nuchal translucency screening is actually a pretty exciting time in your pregnancy. During the exam, you will be able to catch the first glimpse of your growing baby. Your technician may turn the screen, so you can see your baby’s arms, hands, feet, spine and possibly even the face. Some deficits in the abdomen and skull may be able to be seen at this exam, but you will most likely have another scan for anomalies at around your 20th week of pregnancy.

It is a good idea to take one person along with you to the exam such as your spouse, partner or parent as a support person.

How Accurate Is the Nuchal Screening Test?

The NT scan is actually quite accurate, but the most accurate diagnosis is made with a combination of ultrasound scan and the blood test for free beta-HCG, and the protein PAPP-A.

The NT scan only can diagnose about 75% of Down Syndrome cases. There are about 5% of women screened that resulted in a “false positive” for Down Syndrome or 1 in 20 women. This means the NT scan is only suggestive that there is a risk for the condition.

When the scan is combined with the blood tests free beta-HCG and PAPP-A then the accuracy rate of the screening goes all the way up to 90%. In the past, the blood test was performed first and followed by a scan if the results of the blood testing were abnormal. Recently, doctors may just order both tests to be done together.

What Should I Do If I Am at High Risk?

Even if you have been placed in the “high risk” category, knowing the statistics are in your favor. The “high risk” category statistics show that only 1 in 150 women will have a baby with Down Syndrome. That is 149 chances that you will not have a baby with Down Syndorme. Even if they place you in a very high risk category with as little as 1 in 5 chances, there are four chances that you will not have a baby with Down Syndrome.

Regardless of the statistics for you, it can still make you feel very nervous and emotional about your pregnancy. You may also question which steps you should take next. Before you get too nervous and confused over a positive NT scan, know that the only positive diagnostic tool is a chronic villous sampling or an amniocentesis done. These tests take a small sample of amniotic fluid and test for the actual chromosomes in the baby. You may have a hard time making the decision to move forward with these tests since they are invasive.

Since the NT scan is done in the first trimester of pregnancy and an amniocentesis can wait until the 15th week of pregnancy, you have some time to decide if you want the invasive testing done. The best way to decide is to ask lots of questions during your doctor visits and do your research. Only you will know what is best for you and your unborn baby.

All Categories