Figure 13b. Increased NT thickness at 12 weeks gestation associated with trisomy 21. (a) Sagittal transvaginal US image of a fetus with trisomy 21 shows an increased NT thickness of 8 mm (cursors). The skin is elevated along the back due to subcutaneous edema. (b) Photograph of another fetus with trisomy 21 shows a subcutaneous fluid collection at the back of the neck (arrow). (Fig 13b courtesy of Eva Pajkrt, MD, PhD, University College London Hospitals, England.)