This test does no harm to the baby (or to anyone in case) as it is the same as a a regular ultrasound. Ultrasound waves are not ionizing radiation (as the X-ray/CAT) so are completly safe.
testing testing... For a larger version, follow this link: http://1.bp.blogspot.com/_NVBVBm4La4M/SlU-X-KS2II/AAAAAAAAAA4/phqnJSmTkc8/s1600-h/docks+test.jpg