the ultrasound does not only monitor the baby but the mom too. it can help with high risk pregnancies, and help identify patients at risk for: pre-eclampsia etc. it can also measure your baby accurately and predict a more accurate birth date!
I remember this movie I saw. It was a comedy. Single late 30s woman wanted a baby so much but she couldn't bear a child due to something with a T-shaped uterus. So her final option was to have a surrogate mother.
And so she went to a company that offered this, said to be the best in her area. The surrogate mother was a scammer along with her live-in partner. Later into her 'supposed' pregnancy they give an ultrasound image of her 'baby' but was actually an edited image of a squirrel taken off the Ineternet. hahaha!