Well every Dr and insurance is different. I've had 5 ultrasounds. They can take a guess of baby's weight by measuring your belly. Plus ultrasounds aren't accurate to see how much your baby weighs.
I only got one to determine sex that was like at 20 some weeks? & all my appts they just check the usual blood pressure, urine heartbeat & size if belly I've already dropped so I'll b a little pissed if I don't get checked I'm just anxious to know her weight & size & that she's coming along fine! Ftm :)
Weekly appointments start at 36 weeks for me and they begin checking for dilation at that appointment. Also for mine which is next week, they're going to test for strep b. My last ultrasound was at 31 weeks. I won't get another one unless medically necessary.