الفهرس 
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Abstract
Summary and conclusion
The incidence of major congenital abnormalities at birth in the general population is 2% to 3%, yet these abnormalities are responsible for 20% to 25% of perinatal deaths and an even higher percentage of perinatal morbidity. Prenatal detection of an anomaly increases the options for pregnancy management, and in select cases the disorder may be amenable to intrauterine treatment. For these reasons, offering routine ultrasound as a screening test for congenital abnormalities is an attractive concept
Polyhydramnios is defined as excess amniotic fluid volume for a given gestation of pregnancy. This is a physiological finding in approximately 1% of pregnancies in the third trimester. 20% of cases of polyhydramnios are associated with fetal abnormality, hence this finding should be investigated thoroughly when it is detected
However in order to ensure that NO defect is overlooked, a detailed anatomical survey is required. The sonographic examination begins at the fetal head and works caudally down the fetal body
In addition to two-dimensional (2-D) images, 3-D and 4-D imaging allow for reconstructed images in planes that were not previously available. This allows for improved visualization of facial anomalies and anomalies of the hands, feet, and spine. Volume imaging can be used to assess the lungs, which is used in fetuses with suspected pulmonary hypoplasia
Three- and 4-dimensional ultrasonography (3D/ 4DUS) has become one of the major modalities used for assessing fetal anomalies. It allows visualization of fetal structures in 3 orthogonal planes at the same time and different characteristics of the same structure
3D/ 4DUS offers diagnostic advantages for most anomalies. This modality could be a powerful adjunct to 2DUS in the prenatal anatomic evaluation of fetuses
Of course, there are some limitations: (1) the viewing direction is limited to that of the probe, so the most desirable direction cannot always be used, and (2) fetal components clearly evident on 2DUS images cannot always be seen on 3D/4DUS images because of the limited scanning angle, resolution, and position and the presence of artifacts. For these imperfect volumes, it is helpful to review 2DUS images, especially in examinations of the fetal heart.
Some have argued that fetal MRI is on its way to becoming an independent rather than an adjunct method in prenatal imaging .However, it is more likely that fetal MRI will lead the way in the field of neurologic abnormalities, both congenital and acquired, and in clarifying equivocal sonographic diagnoses.