Hello, welcome! If you haven't already, please introduce yourself in the introductions thread. You can wear whatever you would like to an ultrasound. If you are getting an early ultrasound (6-7 weeks) they may do a transvaginal ultrasound and therefore need you to take off your underwear, like a pap smear type situation. If your appointment isn't until later, over 9 weeks or so, then they may only need to access about your pubic bone and above.
Re: What do you wear to ultrasounds?