Normal Nuchal Translucency at 13 Weeks

At about the 13th week of pregnancy, a nuchal translucency (NT) test is recommended to determine the gestational age of the fetus, whether the pregnancy is single or multiple and if the risk of abnormality, such as Down's syndrome and other chromosomal irregularity, is present.

How It's Performed

• The nuchal translucency test is performed by ultrasound when the bladder is full. Along with a measurement of the fetus to determine gestational age, the ultrasound technician or other health care professional measures nuchal translucency, or the fluid present at the back of the fetus' neck. The test is painless and provides a relatively clear image of the fetus. The medical team uses the nuchal translucency measurement, gestational age, mother's age and whether or not a nasal bone is present to calculate the likelihood of chromosomal abnormality.

Normal Nuchal Translucency

• Average nuchal translucency at 13 weeks gestational age is up to 2.8 millimeters. Nuchal translucency grows daily, so it is important to also get an accurate picture of the gestational age. Generally, a nuchal translucency of 2.8 millimeters with other normal indicators indicates a low risk of chromosomal abnormality.

Increased Nuchal Translucency

• An increased nuchal translucency measurement does not in itself indicate that abnormality is present. Some fetuses with no abnormality have a higher nuchal translucency measurement. The test only indicates the percentage of risk. If the test indicates increased risk, more testing is recommended.