Ultrasound gel is a conductive medium that creates a bond between the skin and the ultrasound transducer. The ultrasound sound waves have a hard time traveling through air, so the gel prevents any extra air space between the probe and your skin in order to create a clear image of the fetus. This is why mothers are also asked to come to their ultrasound with a full bladder in early pregnancy. Between your full bladder and the ultrasound gel working as a coupling agent, the technologist will be able to display a clear image of your baby.