they usually give another one around 32-34 weeks !
I normally end up hearing the heart beat and measuring the dark line on my belly at the appoinment. Then the doctor checks my health and makes sure I'm going ok and talks to me about any problem. That's all
If your pregnancy is going good you most likely won't get another ultrasound. Usually they measure the growth of the baby by measuring your uterus. If you have a 3d ultrasound then they will measure the baby.
I've always only had the one to establish pregnancy and the one to determine the sex and scan the anatomy. With my second I had an extra one at 41 weeks just because I was overdue and they wanted to check the health of the baby. Other than that I think in the US, for a healthy pregnancy 2 is all you get.
Ultrasounds always depend on need if high risk or not also insurance and doc if ur pregnancy is healthy u may not get another one they will simply measure belly with tape measure and from that they some how get the weight
I'm not a 100% on this but I don't think they usually do another ultrasound as long as everything seems to be measuring right I think if things seem off they may do one. Again I'm not a 100% sure ask your ob or nurse.
I had one at 26 and a half weeks to check on my baby's heart because my 20 week ultrasound was not quite clear my doctor did say that it was an extra ultrasound.
Not really sure how they know weight but they do start measuring belly with the tape measurement at this point