Hi Linh,
To be honest this probably doesn’t need an ultrasound at all,
If the uterus is prolapsed by such a degree it is a clinical diagnosis and the gynaecologist team can manage the patient medically and surgically as appropriate.
If you do a trans perineal scan I use a convex transducer like i use for imaging the liver etc. I put gel on the transducer and then place a sterile plastic bag over the transducer. Then more gel on the outside. The el on the outside is a sachet of sterile gel, however you are not scanning in a sterile field anyway.
When I finish the scan I remove the plastic bag and wash the transducer in warm soapy water. Then I dry it and sterilise it in a Trophon machine (nannosonics product) then it is ready to be used again.
On the trans perineal study during valsalva you will observe the cervix and uterus undergoing abnormal descent towards the transducer.
If there is a cystocele you will also see the bladder neck anterior to the vagina descending below the level of the symphysis pubis and if it is a cystourethrocele the urethra will rotate into a more vertical position (parallel to the transducer face) as the bladder neck descends.
If there is a rectocele you will see the anterior border of the rectum adjacent to the recto-vaginal septum bulging anteriorly during valsalva.
In my experience with such a large uterine prolapse the other pathologies in the anterior and posterior compartment will be difficult to assess due to the space occupying effect of the prolapsed uterus.
Steve