Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 52

Second‐trimester sonography can also detect a range of minor features or “markers” suggestive of aneuploidy. These are not structural abnormalities of the fetus per se but are associated with an increased probability that the fetus is aneuploid. These minor markers are typically much more common than structural abnormalities and likelihood ratios based on the presence or absence of these markers have been used to adjust each patient’s risk of having a fetus with trisomy 21. However, with improvements in aneuploidy screening, including serum and combined methods as well as cfDNA screening, these minor findings add little to the detection of chromosomal abnormalities. Rather, when screening results indicate a low risk of aneuploidy, these markers are most commonly normal variants. The one possible exception is a thickened nuchal fold, which is uncommon in euploid fetuses and therefore has a low false‐positive rate and relatively high specificity for Down syndrome. In cases in which multiple markers are seen, the risk of aneuploidy is higher and genetic counseling may be indicated. Table 5.2 also summarizes the minor sonographic markers that, when visualized, may increase the probability of an aneuploid fetus.