High-Risk Pregnancy

Nuchal Translucency Screening

What is nuchal translucency?

Ultrasound done between 11 weeks 4 days and 14 weeks 3 days will measure the fluid accumulation behind the neck of the baby, called the nuchal translucency (NT). Extra fluid, (an increased NT) can be a sign of Down syndrome, trisomy 18 or trisomy 13.

Why is it called "screening"?

Screening only provides an estimate of risk. A positive result, indicating an increased risk, does not mean the baby has a problem. Diagnostic testing, such as chorionic villus sampling (CVS) or amniocentesis, is the only way to determine with certainty if a baby has Down syndrome, trisomy 18 or trisomy 13. A negative result, indicating a lower risk, does not eliminate the risk that the baby will have Down syndrome, trisomy 18 or trisomy 13.

First trimester screening detects about 85% of pregnancies in which the baby has Down syndrome and 91% of pregnancies in which the baby has trisomy 18.

Who should be offered this screening?

Women of all ages can consider the option of first trimester screening. If a woman will be younger than 35 at delivery, she will attend an educational session prior to her NT screening.

If a woman is 35 or older at delivery, she will be scheduled for genetic counseling to review all diagnostic and screening options, including CVS, amniocentesis, and first and second trimester screening.

What are the advantages of first trimester screening?

First trimester screening has a higher detection rate than second trimester screening. This means that if a baby has Down syndrome or trisomy 18, the first trimester screening is more likely to detect the problem.

First trimester screening is done earlier in the pregnancy and can give couples important information as early as possible.

Increased nuchal translucency has also been associated with other fetal anomalies such as cardiac defects. A second trimester fetal anatomy ultrasound and echocardiogram are recommended if the NT is increased.

What are the limitations of first trimester screening?

Risk figures can only be calculated for Down syndrome and trisomy 18/trisomy 13. 

First trimester screening does not assess a risk for neural tube defects.  All women will continue to be offered second trimester screening for neural tube defects through the state XAFP program.

First trimester and second trimester screening may produce different results, thus making the decision to pursue diagnostic testing difficult.

How long do results take?

Results will be available in approximately 1 week.  The patient will be called directly and her physician will receive a report of the results.