During in utero development, fluid -- known as nuchal translucency -- naturally accumulates at the back of a baby's neck. Measuring nuchal translucency when the foetus is 10 to 13 weeks old can help determine if the baby may suffer from Turner or Down syndrome. An increased amount of fluid detected during an ultra sound can indicate an increased risk for such disorders.
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The Greater Baltimore Medical Center states that 20 to 60 per cent of babies who have an increased nuchal translucency level may suffer from a chromosome abnormality. Turner and Down syndrome infants usually display more fluid on an ultrasound scan. The detection of an increased amount of fluid often helps determine if additional diagnostic tests, such as chorionic villus sampling or amniocentesis, should be performed. Nuchal translucency measurements are usually done in combination with maternal serum information for the First Trimester Screening tests.
When the foetus reaches 13 weeks old, the baby's lymphatic system begins to reabsorb the fluid. By 14 weeks, the baby's body has successfully absorbed the fluid. Approximately 80 per cent of babies suffering from Trisomy 21, also called Down Syndrome, show an increased nuchal translucency, according to the Department of Obstetrics and Gynecology, Prenatal and Preimplantation Genetic Diagnosis, and the Croatian Medical Journal. The ultra sound used to detect nuchal translucency also helps determine the true gestational age of the foetus. The technician performing the scan measures the fluid accumulation and looks closely at the brain, limbs and abdominal wall to detect any abnormalities.
Normal and Abnormal Measurements
A normal nuchal translucency level measures 2.0mm or less at about 11 weeks. The fluid measurement generally rises to 2.8mm by 13 weeks. Some babies who have no abnormalities may show an increased nuchal translucency measurement. A baby's nuchal translucency can measure as high as 2.5mm and 3.5mm, but have no disorders. As the measurement levels increase, the risk of chromosome abnormalities rises. A nuchal translucency measurement of 6mm holds extremely high risk that the baby will suffer from Down Syndrome, according to the Womens Fetal Imaging Center.
An increased nuchal translucency usually indicates a chromosome abnormality, but it can also occur in an infant suffering from a heart abnormality. An increase in nuchal translucency occurs in approximately 5 to 20 per cent of babies suffering from a congenital heart defect, according to the Greater Baltimore Medical Center. If chromosome abnormalities are ruled out through chorionic villus sampling or amniocentesis after an abnormal nuchal translucency measurement, the patient should have a fetal echocardiogram. The echocardiogram helps determine if the heart may suffer a defect.
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- Greater Baltimore Medical Center: Nuchal Translucency
- BabyCentre: Nuchal translucency (NT) scan
- Croation Medical Journal; Nuchal Translucency and Nasal Bone for Trisomy 21 Screening: Single Center Experience; Giovanni Monni, et al; 2005
- Womens Fetal Imaging Center: 12-13 Weeks Ultrasound Scan
- U.S. National Library of Medicine; Elevated First-trimester Nuchal Translucency Increases The Risk of Congenital Heart Defects; Bahado-Singh RO, et al.; May 2005
- The New England Journal of Medicine; Increased Nuchal Translucency as a Marker for Fetal Chromosomal Defects; Pekka Taipale, M.D, et al.; 1997