Although ultrasound does not have the same dangers to human health on the fetus as radiation does it is wrong to think that ultrasound is completely safe for the baby growing in your womb.
Ultrasound scan works by sending sound waves to your tissues. As these sound waves bounce off your tissues, creates a picture.
These sound waves are able to create the following physiological effects:
Increase blood flow and temperature in the local tissues
Creating bubbles that can put pressure on local tissue
Mechanical effects such as movement of fluids around your cells, which also causes pressure on local tissue