Substances that enter the body in the nature of food or drink invalidate the fast. A transrectal ultrasound does not, in principle, invalidate the fast, as it does not constitute eating or drinking. However, if water is introduced through the device during the procedure, the fast is invalidated. If, during the ultrasound, no water, oil, or any substance with nutritive value enters the digestive system, undergoing a transrectal ultrasound does not affect the fast.
Since the female reproductive organs are not part of the digestive system, transvaginal procedures such as uterine ultrasound, gynecological examination, smear testing, or biopsy do not invalidate the fast.
In endoscopy performed to examine gastric diseases, a device is introduced through the mouth into the stomach and removed after the procedure. In colonoscopy, which is performed to diagnose intestinal diseases, a device is inserted through the rectum into the intestines and likewise removed after the procedure. In colonoscopy almost always, and in endoscopy in most cases, water is introduced through the device in order to clear the field of view.
For this reason, although procedures such as endoscopy, colonoscopy, or transrectal/transvaginal ultrasound are not considered eating or drinking, they often invalidate the fast because water is introduced, and a make-up fast (qaḍāʾ) becomes necessary. However, if during the procedure no water, oil, or any substance with nutritive value enters the digestive system, none of these procedures are considered to invalidate the fast.