![]() The First and Second Trimester Evaluation of Risk (FASTER) trial showed that screening with NT-based US is even more efficient when combined with maternal serum-free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A, increasing detection rates to 87% at a 5% false-positive rate.Īn increased NT measurement is not uniquely associated with trisomy 21. Major prospective studies from the United States and Europe have confirmed that US performed for NT is a powerful prenatal marker for Down syndrome, with detection rates ranging from 63% to 77% with a 5% false-positive rate. As a result, first-trimester US to assess NT has evolved from an imaging evaluation used in a research setting to a screening tool that is widely available to the general obstetric population. An increase in NT is now recognized to be an early presenting feature of a broad range of fetal chromosomal, genetic, and structural abnormalities. In the early to mid-1990s, ultrasound (US) evaluation in the first trimester revealed an accumulation of subcutaneous fluid behind the fetal neck that could explain the apparent excess skin this finding became known as nuchal translucency (NT). In 1866, Down first reported an accumulation of excessive skin in individuals with trisomy 21. As such, conventional screening with ultrasound (US) for NT remains the most appropriate choice for first-line screening in the general obstetric population. Conventional screening methods with serum analytes and NT measurements are more likely to detect other chromosomal abnormalities, as well as the risk of other adverse pregnancy outcomes. Additionally, trisomies 13, 18, and 21 represent a lower proportion of the chromosomal abnormalities that occur in this group compared with older women. The lower prevalence of aneuploidy in younger, low-risk women increases the false positive rate in this particular population. In high-risk obstetric populations, it is recommended that this form of testing now be offered as a first-line screening option. Noninvasive prenatal screening using maternal cell-free DNA (cfDNA) is rapidly transforming prenatal screening, with all tests providing a high sensitivity and specificity for trisomies 21 and 18. NT is also often increased in fetuses with a variety of other genetic conditions, including trisomies 13 and 18, Turner syndrome and triploidy, as well as structural birth defects such as congenital heart defects. The combination of NT with serum markers in the first trimester detects 87% of cases of Down syndrome for a 5% false-positive rate. ![]() Nuchal translucency (NT) measurement in the first trimester is a powerful marker for Down syndrome. All women should be offered prenatal screening or diagnostic testing for aneuploidy, regardless of maternal age, but with the increasing number of prenatal screening options now available, deciding which is the most appropriate test is increasingly complex. ![]()
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