2D and 3D Ultrasound in the evaluation of normal and abnormal fetal anatomy in the second and third trimesters in a level III center.

Between July 2000 and December 2003, a total number of 3,472 fetuses was evaluated by two-dimensional (2D) and three-dimensional (3D) ultrasonography. All examinations were carried out as part of a detailed level III ultrasound examination for fetal anomalies. The gestational age was between 11 and 35 weeks. A 3D endovaginal probe (5 - 7 MHz) was used for examinations between 11 and 13 weeks, and an abdominal 3D probe (5 MHz) after 13 weeks. Four different 3D image display modes were employed in visualizing fetal malformations: triplanar orthogonal display; surface display; transparent display; and the combined transparent and color display (= glass body-rendering). In 906 of the 3,472 high-risk pregnancies, fetuses with one to five fetal defects were found (mean 1.17). The total number of detected defects was 1,012, exclusive of 48 fetal heart defects. Fetal heart defects were excluded from this study since a reliable demonstration of these defects was not possible by 3D ultrasound. Comparing the 2D and 3D techniques, 3D sonography proved advantageous in 60.8 % of the defects, with the benefit derived from the exact tomographic survey using the multiplanar view in 69.9 % of these cases, from a more precise demonstration of the defect in the surface view in 25.2 %, from a distinct demonstration in the transparent view in 3.9 %, and from a precise demonstration in the combined transparent and color view in 1.0 %. In 42 of the 1,012 malformations (4.2 %), a defect was accurately identified or verified with 3D ultrasound only. 3D ultrasound proves not only a useful tool in appreciating the severity of a fetal defect, but also provides more convincing evidence of a normal fetus than conventional two-dimensional sonograms in cases with increased risk of a recurrent surface malformation.