To dream of witnessing an ultrasound suggests that you want information about someone that may not be your right to have. You may not be entirely satisfied with the information that you do have and feel the need to know more. Dreaming that you are receiving an ultrasound is more emotionally significant in that you may be wishing to uncover some insight into your own emotional world.
The potential for a positive emotional shift is apparent here.... Dream Symbols and Analysis
If you dream about having an ultrasound, you are worried that someone you weren’t completely truthful with will find out about your deception. You may also be keeping something secret because you’re not ready to talk to people about it yet.... My Dream Interpretation