Promises and pitfalls of first trimester sonographic markers in the detection of fetal aneuploidy

First trimester sonographic markers are the only markers achieving detection rates above 50% in the prenatal detection of fetal aneuploidy. Although potentially they are the best markers, some concerns have arisen about its clinical application. Pitfalls may be due to inability to examine the markers, incorrect assessment, or incorrect interpretation of the findings. Markers may be unable to be examined due to maternal (maternal body habitus, previous surgery) or fetal reasons (incompatible fetal position or fetal movements). Causes of incorrect interpretation may be insufficient image magnification, incorrect caliper placement (nuchal translucency), incorrect insonation angle (nasal bone), venous contamination (ductus venosus), or arterial contamination (tricuspid regurgitation), among others. Venous contamination in ductus venosus waveforms may mimic an abnormal blood flow when it is normal, and the opposite can also occur. Finally, incorrect interpretation of a substantially increased nuchal translucency may lead to a false impression of an ominous fetal prognosis or may be confounded with a cystic hygroma. Copyright © 2008 John Wiley & Sons, Ltd.     

The history of the second-trimester sonographic markers for detecting fetal Down syndrome,and their current role in obstetric practice

This review summarizes the development, history and use of second-trimester sonographic markers for the detection of fetal Down syndrome over three decades. Starting with the nuchal fold thickening in 1985 and culminating in the genetic sonogram in the 1990s. The combination of second-trimester serum screening with the ultrasound markers improved the detection rate of affected fetuses but also allowed patients to decrease their risk of carrying a fetus with Down syndrome if the genetic sonogram was normal. More recently the role of the genetic sonogram and its markers have changed with the wide spread use of first-trimester screening. This prior screening ultimately decreases the prevalence of fetal Down syndrome in the second trimester to less than 85% of what it was in the first-trimester as most fetuses with Down syndrome are now identified early. Current interpretation of the second-trimester Down syndrome markers must be based on the result of the first trimester and combined screening to achieve the most accurate risk estimate of an affected fetus. Copyright © 2010 John Wiley & Sons, Ltd.