Ultrasound
Often, the purpose of an ultrasound is to determine the status of the fetus, and when necessary doctors will recommend an abortion. Since in most cases according to Halacha an abortion is not acceptable, the ultrasound will only cause anxiety and anguish to the parents. Another issue with an ultrasound is the fact that if there is a problem with the child, so long that we are not aware of it, our Tefilos and Bitachon can make sure that everything is fine. Once mankind is aware of the problem, then a Nes, a miracle, is required to change the status. Also, according to the Medrash, there are things that human beings are not meant to know, including whether the baby is going to be a male or a female. There are also medical issues with routine ultrasounds - and the risks versus the benefits need to be carefully analyzed. These issues are beyond the scope of this discussion. Of course, in a case where doctors recommend an ultrasound for a medical need, normally a Rov would permit it.
https://halacha2go.com?number=63