I haven't had mine yet but 2 of my friends got theirs at 25 or 26 weeks!
Got mine @ 28 weeks. And having another monday and im 33 weeks. the later In pregnancy, the better the ultrasound
I had a private one at 16 weeks so I could find out the gender sooner.
They tried mine at the 20 week ultrasound but she wasn't cooperating. They tried again around 28weeks but again she was facing downward and away from us:/