Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 49
Secondary sonographic markers
ОглавлениеWhile measurement of the NT combined with serum markers has been the mainstay of general population screening for many years, other sonographic features of aneuploidy have also been reported in the first trimester. Cystic hygroma is reported in about 1 of every 300 first‐trimester pregnancies, and refers to a markedly enlarged NT, often extending along the entire length of the fetus, with septations clearly visible. While it is not clear that a cystic hygroma is distinct from a markedly enlarged NT, this finding is associated with a 50% risk for fetal aneuploidy and in the remaining euploid pregnancies, almost half will be found to have major structural fetal malformations, such as cardiac defects and skeletal anomalies. Less than 25% of all cases of first‐trimester septated cystic hygroma or markedly enlarged NT (e.g., ≥6.5 mm) will result in a normal liveborn infant. Therefore, this finding should prompt immediate referral for CVS, and pregnancies found to be euploid should be evaluated carefully for other malformations with a detailed fetal anomaly scan and fetal echocardiography at 18–22 weeks of gestation, or in the first trimester if such evaluation is available.
Figure 5.3 Nasal bone image of a euploid fetus at 13 weeks. Various features of good nasal bone technique are evident in this image: a good midsagittal plane, clear fetal profile, downward‐facing spine, slight neck flexion, and two echogenic lines, representing the overlying fetal skin and the nasal bone. The white arrow indicates the fetal nose bone, which loses its echogenicity distally.
Source: Mary E. Norton, MD.
Other sonographic features that have been reported to be useful in detection of trisomy 21 at 11–14 weeks include an absent nasal bone (Figure 5.3), an abnormal Doppler blood flow pattern in the ductus venosus, and abnormal blood flow across the tricuspid valve with evidence of tricuspid regurgitation. However, studies suggesting a role for aneuploidy screening using these sonographic evaluations in the first trimester have been derived from select high‐risk populations, and likely overestimate the screening performance. At this time, while evaluation of the nasal bone can be useful for risk stratification in cases with enlarged nuchal translucency, first‐trimester evaluation of these other secondary markers is not recommended for general population screening.