I'm 35 Weeks Pregnant With Twins. During An Ultrasound, Nurse

I'm 35 weeks pregnant with twins. During an ultrasound, nurse found a mass just outside my uterus. I declined to get an mri and catscan due to my belief that it is dangerous to the babies. Since, I will have a c-section doctors suggest they should do an investigative surgery on the day of the c sectionjust to see what it is. I am also declining this. I prefer to see a specialist and focus on this after my babies are born. I feel like I'm getting pressured to do this extra surgery.