Alternative Names
NT
Symptoms & Characteristics
Nuchal translucency (NT) refers to the collection of fluid under the skin behind the baby's neck during first trimester development. The amount of this fluid is typically measured between approximately 11 and 14 weeks of pregnancy. All babies have some fluid under the skin at the back of the neck, but a higher than expected amount increases the concern for the baby to have some kind of birth defect or genetic condition (such as a chromosome abnormality or other genetic condition); there also is an increased risk for fetal death and stillbirth. It is important to note that an NT measurement can only estimate the risk for a baby to have a birth defect or genetic condition; it does not definitively diagnose a condition.
The NT measurement varies with the gestational age of the pregnancy. The NT measurement is performed between 11 and 14 weeks of pregnancy because, at that time, the baby's lymphatic system is developing and the peripheral resistance of the placenta is high. After 14 weeks of pregnancy, the lymphatic system of the baby is likely to have developed sufficiently to drain away any excess fluid, and changes to the placental circulation will result in a drop in peripheral resistance. Therefore, after 14 weeks of pregnancy, any abnormalities causing fluid accumulation may seem to correct themselves and can consequently go undetected by measuring the NT.
Treatment
The overall prognosis and management is dependent upon the cause of the increased NT measurement.
How Common Is It?
All babies have some fluid under the skin at the back of the neck. An accurate estimate of the amount of pregnancies shown to have an increased NT measurement is not available. Even babies with an increased NT can be healthy.
Genetics & Inheritance
Conditions known to be associated with an increased NT measurement include (but are not limited to): chromosome abnormalities (i.e. Down syndrome, Trisomy 18, Trisomy 13, Turner syndrome), cardiac (heart) defects, Noonan syndrome, Roberts’ syndrome, numerous metabolic disorders, twin-to-twin transfusion syndrome (only in the case of a twin pregnancy), numerous skeletal dysplasias and Meckel-Gruber syndrome. It is important to note that this list is not exhaustive.
An evaluation by a genetic professional and perinatologist may be helpful in possibly determining the cause of the increased NT measurement in the baby. This is important for not only the health and management of the pregnancy but also for an accurate estimation of recurrence risk within a family.
Genetic Testing
A first trimester ultrasound between 11 and 14 weeks of pregnancy should be performed by a certified practitioner for accurate NT evaluation and measurement. Should an increased NT be noted, the availability of prenatal testing can be discussed with a genetic counselor and/or a medical geneticist. For more information about screening options and genetic testing options during pregnancy see: Genetic Testing in Pregnancy.
It is always recommended to see genetic counseling with a trained genetic professional for a complete evaluation, accurate diagnosis, and discussion of the benefits and limitations of testing and recurrence risk. Use our find a genetic professional directory to locate a trained genetic professional in your area.
Support & More Information
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