Pregnancies where the nuchal translucency measurement is between about 2.5 and 3.5 mm are in an intermediate-risk group, and for these women, a genetic sonogram at about 18 weeks into the pregnancy plus a detailed sonogram of the heart (called a fetal echocardiogram) at about 22 weeks are recommended. A very small nuchal translucency measurement – less than 2.5 mm – places the pregnancy in a low-risk group for problems, such as fetal heart abnormalities. The nuchal translucency measurement is more than just a screening for Down syndrome. It is important to realize that the only way to be certain that a baby does not have a numeric chromosome abnormality like Down syndrome is by means of Amniocentesis or Chorionic Villous sampling. The state requires that all first and second trimester blood specimens are performed in the state laboratory system. In the State of California, there is a prenatal screening program which is used for risk calculations. Approximately 5-10% of the time, we are unable to obtain this measurement either because the baby does not cooperate or there are other technical factors like abdominal wall scarring, fibroids or maternal obesity. The nuchal translucency screen will identify 85-90 percent of Down syndrome cases and 80-85 percent of Trisomy 18 cases. Women who screen positive at increased risk would then be offered further testing. If we can accurately measure the nuchal translucency, then a computer program can be used to calculate the risk for Down Syndrome and Trisomy 18 using the mother’s age and blood hormone markers. We use this measurement as an early screening tool to identify pregnancies at higher risk for these conditions. Between 11 and 14 weeks of pregnancy, this space can be measured by ultrasound and the size of this space is associated with the risk for fetal chromosome abnormalities and the risk for fetal heart defects. Nuchal Translucency Screening for Detecting Trisomy 21 (Down Syndrome) and Trisomy 18.ĭuring development of the embryo, there is a clear space beneath the skin at the back of the neck which we call the nuchal translucency. This test has about an 85 % detection rate for Down Syndrome. Additional testing and counseling would be recommended if the test is positive. It is part of the California Prenatal Screening Program and is a free service to all pregnant women. Nuchal translucency/First trimester screening – this blood test screens for Down Syndrome (Trisomy 21) and Trisomy 18. In addition, at San Diego Perinatal Center, with our high resolution equipment, we are able to detect 40% of major fetal anomalies such as neural tube defects, abdominal wall defects, renal, limb and cardiac abnormalities on this early scan. This scan can be used to accurately date your pregnancy, to evaluate abnormalities in your ovaries and cervix, to accurately determine chorionicity in twins, to assess for placental abnormalities and to perform a nuchal translucency screen. First trimester ultrasound performed between 11 and 14 weeks is an important early assessment of your pregnancy.
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