A nuchal translucency scan is a prenatal ultrasound scan that helps detect various defects, such as chromosomal abnormalities, during early stages of pregnancy.
This test is recommended to all pregnant women as part of prenatal screening tests, regardless of maternal age or risk factors. The scan is usually preformed in weeks 11-14 of pregnancy. Deviations from this period may affect test results and make them unreliable.
How is the test performed?
This procedure is similar to routine ultrasound scans performed during pregnancy. During the scan, a healthcare professional (such as an obstetrician, midwife, sonographer, or nurse) places an ultrasound transducer on the pregnant woman’s abdomen, focusing on the fetus’ head and neck area.
The scan will show a black area at the back of the fetus’ neck (called the nuchal fold). when performed correctly, the screen shows an enlarged image of the head and neck area. Results indicate the nuchal translucency measurement.
The procedure usually lasts several minutes, this is a low-risk scan that is usually unpainful.
Results are a combination of the nuchal translucency measurement, maternal age, and gestational age. This procedure is performed too early into the pregnancy to determine the baby’s sex.
What do the results mean?
The results of a nuchal translucency scan have statistical use only, and do not hold qualitative significance. A larger than usual nuchal translucency measurement indicates a higher risk for certain birth defects.
Results also depend on the size of the fetus, according to the CRL range.
What diseases can the test detect?
Higher than usual amounts of fluid in the back of the neck indicate a higher risk for Down syndrome, which is the most common chromosomal abnormality. NT scans are an important part in screening for Down syndrome, along with first trimester blood screening, and the triple scan during the second trimester.
The scan can also help detect other chromosomal abnormalities such as Turner syndrome. In this chromosomal disorder, the female fetus has only one copy of the x chromosome instead of two. A male fetus will have an extra Y chromosome. Women with Turner syndrome often suffer from infertility and other defects.
The nuchal translucency scan can also help detect other chromosomal abnormalities including trisomy 18 and trisomy 13.
It is important to point out that nuchal translucency scans do not diagnose diseases. After receiving abnormal scan results, women are usually referred to further tests, such as amniocentesis, for a more accurate diagnosis.
Amniocentesis is an invasive procedure in which fetal cells are sampled for a more definite identification of genetic disorders. The pregnancy can also be monitored through other ultrasound scans, such as an anomaly scan (anatomy scan).