Is a growth ultrasound normal?

My doctor ordered one for me at 36 weeks. I'm not high risk, and every visit when they measure my tummy I am either ahead or on track. I saw online people say it's only offered if you're high risk or not measuring right. I didn't think much of it when she told me I would have one. I thought it was normal. Anyone else just get ordered one just to check weight because it's normal?