Doppler ultrasound-fertility treatment

Kelly
I'm going to get sonohysterography done on Friday.( I failed 4 <a href="https://glowing.com/glow-fertility-program">IUI</a> so far)
Dr suggested to do Doppler ultrasound with it and I said ok but I didn't ask why as our conversation went on something else. 
Now here I am home sittting by myself and think if I really should do Doppler ultrasound because it's expensive.
Is it really necessary? Does anyone have experiences?