they measure the belly and the head and get an estimate that way off the screen. It’s not exact, it’s just a guess. I think maybe it has to do with the weight you gain and the fluid measurment as well? it’s something they do over time to compare. The only reason I got measurements is because I am high risk and also had to go in more often, sometimes not scheduled, snd when ever the check makes sure things are fine, she always likes to check everything, just for the “heck of it” she says. “might as well since you are here!” she tells me. Except my when I came in 2 weeks in a row, last week she said “we checked everything your last visit, I’ll just do the basics today”. (i came in due to a reoccurring pain a week before my appointment) So.. at least for me.. no i didn’t have to pay extra, but being high risk it’s costing more eith double to triple the amount of scans I need, plus the few emergency ones. So, it’s a scientific estimate to hand out a number like that, but they DO and always will check to see if the baby’s growth progresses nicely with each scan, even if they don’t have a number, they still check the bowels/organs, femur, skull and such to get a better idea. Therr are some things that seem common for other moms that they never did for me, like measure my belly growth or ask me ti count kicks, and never told me the status of my cervix until like a week ago! So, all doctors and situations are different and some find things important that others see as not needed, some have techs that stay wuiet, some techs tell you everything they see and what they are doing.

Oh right OK. I'm not expecting any more scans (had my 20 week one). I just started getting measured at my last 28 week midwife appointment.

My ob requested a growth scan at 32 weeks because I was measuring small, but my baby girl lays crazy in my belly so sometimes I'm big and sometimes it's like she's dissapeared haha.