weeks They check the spine, heart, kidney, bladder, take measurement of babys size such as skull and I think they do crown to heel measurements rather than crown to rump. Also check
foot for Club
foot and measure femur bone. They do do a lot of checking but dont worry its precautionary for the most part. Theu do watch the heart beat and examine of course to make sure all os developing correctly. Its actually neat to see the babys spine and heart etc. good luck!