How does your doctor measure baby?

I’m 10 weeks now, and had my first appt last week with the gynecologist, as well as an ultrasound. The doctor explained that with overweight women, measuring the fetus can be difficult by measuring the woman’s belly, and that having an ultrasound each time is his recommendation. I’m not going to do that. It sounds unnecessary and expensive to me. I’m getting a second opinion anyways, but I wanted to hear experiences from other overweight pregnant mothers about how their doctors measured their pregnancies.