They could be referring to their fundal height - the tape measure they use to measure from your pubic bone to the top of your uterus. But it can be pretty inaccurate
It depends on the pregnancy, in normal pregnancies they usually do one at 36 weeks if they feel like it needs to be done, some people don't even get one. I have had growth scans every 4 weeks since week 20, so 24, 28, 32, and 36 weeks is when I have them, plus with my son they did extra at the end because he was big. For me it's because of my BMI, I'm also having twins this time so that's an extra reason but I would be getting them either way because of my BMI.
Depends on the provider because I’m only 30 weeks and have had two due to being high risk.