unless you are pregnant and your doctor is measuring your fundus (uterus) or you are suspected of having ascites (fluid in your abdomen as a result of liver disease) there are only a few reasons why a clinician would be measuring your abdomen. it is never a part of a routine general exam. since i don't know the medical details it is difficult to offer any rationale. i suggest that you specifically ask the doctor -- the one who is doing the measuring -- for the reason.
what does it mean when the doctor measures your belly?