Why the full bladder for an ultrasound?
The reason for this is that the fluid in the bladder creates a “window” for the beam to pass through. (This provides a good medium for sound conduction.) It also serves as a “landmark” for the technician to get their bearings, so to speak. In addition, a full bladder can change the position of the uterus, taking the flexion out of it and pushing it up so it is easier to scan. A full bladder also moves loops of bowel up and out of the way to make the pelvic organs easier to view. In later pregnancy, or with a transvaginal approach, (the probe is introduced into the vagina), a full bladder is not necessary. The enlarging uterus is quite nicely positioned above the pubic bone and the fluid within the sac provides the medium for passage of the beam.
