What my midwife said about ultrasounds is, "If they had a really bad effect, you'd be seeing a lot of damaged kids walking around. Especially with multiples and high risk pregnancies, some of those women get gobs of ultrasounds." (She did say 'gobs,' too.) Yeah...true enough, I guess, but on the other hand, there is some evidence that the sound waves can heat the cells, and I think it's prudent only to do them for medically indicated reasons, not just to get baby photos or find out the sex or to have a "keepsake video." Here's
an article from Mothering Magazine that discusses this further. If you have questions, do your research, make sure you are giving truly informed consent to the procedure.
The womb doesn't have a window, and there is something really sacred about that unseeable interior space where new life is forming. I think it honors that space to leave it a mystery, but it's really hard to get away from that impulse to KNOW WHAT'S GOING ON IN THERE!