US Pregnant Uterus Transvaginal Transvaginal US may be utilized for first trimester aneuploidy screening if optimal views of the nuchal translucency cannot be obtained using the transabdominal approach, which occurs in about 5% of patients [5,24,28]. The higher resolution of transvaginal US can be particularly helpful when imaging women with high body mass indexes. The transvaginal approach may also be favored in patients with multiple abdominal surgeries or presenting with a transverse fetal lie in the lower aspect of the uterus. However, reduced probe mobility limits the available image planes, so using a combination of transabdominal and transvaginal US may be necessary to fully assess the first trimester fetus. Fetal nuchal translucency measurements are similar whether measured by transabdominal or transvaginal US as long as the same principles for image acquisition and nuchal translucency measurement are applied [29]. The transvaginal approach may produce better quality images to assess the nasal bone than transabdominal US [65]. However, perhaps because of the restricted range of movement, a 3-fold higher failure of nasal bone imaging has been reported with transvaginal US [30]. If there is difficulty obtaining the nuchal translucency measurement, there is likely to be difficulty in obtaining the proper image to assess for the presence or absence of nasal bone regardless of approach. The ductus venosus can be easily identified by its accelerated flow velocity on color Doppler and then interrogated with pulsed Doppler to assess its flow characteristics. The triphasic waveform of the ductus venosus, reflecting the phases of the cardiac cycle, normally has forward flow toward the heart at all times; a reversed a-wave, corresponding to retrograde flow during atrial contraction, is abnormal.
Nuchal Translucency Evaluation at 11 to 14 Weeks Gestational Age. US Pregnant Uterus Transvaginal Transvaginal US may be utilized for first trimester aneuploidy screening if optimal views of the nuchal translucency cannot be obtained using the transabdominal approach, which occurs in about 5% of patients [5,24,28]. The higher resolution of transvaginal US can be particularly helpful when imaging women with high body mass indexes. The transvaginal approach may also be favored in patients with multiple abdominal surgeries or presenting with a transverse fetal lie in the lower aspect of the uterus. However, reduced probe mobility limits the available image planes, so using a combination of transabdominal and transvaginal US may be necessary to fully assess the first trimester fetus. Fetal nuchal translucency measurements are similar whether measured by transabdominal or transvaginal US as long as the same principles for image acquisition and nuchal translucency measurement are applied [29]. The transvaginal approach may produce better quality images to assess the nasal bone than transabdominal US [65]. However, perhaps because of the restricted range of movement, a 3-fold higher failure of nasal bone imaging has been reported with transvaginal US [30]. If there is difficulty obtaining the nuchal translucency measurement, there is likely to be difficulty in obtaining the proper image to assess for the presence or absence of nasal bone regardless of approach. The ductus venosus can be easily identified by its accelerated flow velocity on color Doppler and then interrogated with pulsed Doppler to assess its flow characteristics. The triphasic waveform of the ductus venosus, reflecting the phases of the cardiac cycle, normally has forward flow toward the heart at all times; a reversed a-wave, corresponding to retrograde flow during atrial contraction, is abnormal.