the occipital bone and the cerebellum. The measurement is made from the outside of the occipital bone to the skin edge and is considered thickened at 6 mm or greater (Figure A). Although most centers use 6 mm as the measurement for abnormal nuchal thickness, some other authors use 5 mm or greater. This measurement improves sensitivity but increases the number of false-positive examinations. Absent or short nasal bone is one of the most promising newest markers. For correct evaluation of the nasal bone in the second trimester, it is important that the angle of insonation be 90 degrees from the longitudinal axis of the fetal nose (Figure B). An individual with Down syndrome has a short stature with a short femur and humerus (Figure B). These are considered minor markers because of their prevalence in the normal population and vari­ability in different ethnic groups. Hyperechoic bowel is dened as fetal bowel that is as echogenic as bone. However, this is a subjective nding and difcult to use because echogenicity of fetal bowel is affected by transducer frequency and machine settings. EIF is identied as an echogenic focus that is as bright as bone and best detected when the heart is vertically aligned with the ultrasound beam (Figure C). Pyelectasis in a second­trimester fetus is dened as renal pelvis AP dimension 4 mm or greater in transverse plane.