Ultrasounds were only used when there was concern when I was having my boys.
I had to go 90 miles with a full bladder in the fourth month for an ultrasound for the first because they thought I might be having twins (I kind of exploded outward between 3 & 4 months) but nope...just one, growing fast.
When I did the same thing in my second pregnancy and they suggested another trip to Spokane, I passed.
A friend had one done around the same time, and the technician told her she was having a boy, then jokingly added "or a deformed girl". She worried for the rest of her pregnancy, and when she gave birth and the OB said it was a girl, her husband says she got absolutely hysterical in the delivery room. The OB thought there was some normal hormonal swelling that the tech interpreted as a penis...no deformity.
The technology has improved vastly since then, but it still amazed me when my daughters & DIL's were getting them practically every six weeks...