Unnecessary ultrasounds?

Jen • I'm 34 with b/g twins via IVF FET, born 11/2016. Had a mc after first IVF/FET, 3 failed IUI, mild endo. 1% morphology
Shocked at a recent bill from the maternal fetal medicine group that did my 20-week level 2 ultrasound, I'm now wondering what is a normal schedule for level 2 ultrasounds with a twin pregnancy. What was your experience? How many did you have after 20 weeks? My OB has me going in for another tomorrow (26 weeks) to "check on growth." I have b/g twins and have had no complications so far, except a subchorionic hemorrhage earlier in the pregnancy, which has cleared.