A Spinning Babies visitor- "I along with many women, would greatly appreciate any info you could provide as to what to do during pregnancy and especially during the pushing phase that would prevent pelvic organ prolapse (rectocele, cystocele, uterocele, etc.) from occurring, or at least help keep any current prolapse from worsening."
For your pelvic floor protection:
No caffiene (yes!)
Regular inversions, legs-up-the-wall and if you can, shoulder stands
A myofascial pelvic floor release side lying release)
Yoga exercises for pelvic balancing and strengthening
Release of the Psoas muscle pair
In pregnancy the same
plus do the side lying release once in early labor and once during late labor, for instance in the presence of strong contractions but no (slow) progress or after the transition phase before a strong urge to push (if there is a lull then). Any time is fine, but those are examples.
Picture of a side-lying release (pelvic floor release).
A good fetal position for an average size baby is easier on the pelvic floor. Continue a short inversion every day (30 seconds).
In labor, use rotation friendly comfort measures (upright, walking, hands and knees, side-lying when resting and techniques if labor is slow due to fetal position).Keep your bladder empty, especially during pushing.
Push on hands and knees or standing rather than on your back, any position other than on your back if you are not allowed to be on Hands and Knees or upright.
Don't hold your breath and push unless there is no progress due to either asynclitism or a hand in the way, or perhaps just size. (Rather take a little nap if the contractions are spaced, there's no urge insisting upon spontaneous pushing.)
Sit in a deep tub of water for a while during pushing, even if you don't birth in the tub.
Once in a while strong pushing is just necessary, but less likely for a second baby than for a first. Possible, but less likely.
Plus, avoid a pudendal block, epidural, episiotomy, vacuum or forceps! There is a lot of evidence that these things cause more pelvic floor damage. Of course, the vacuum or forceps is reasonable to consider if it avoids a cesarean, but deciding when it is necessary varies among providers. Try a pelvic floor release (again if necessary) if pushing is slow. I realize some women will pick an epidural. I don't want anyone to suffer, but don't deny yourself the support you may need, the preparation that may help, so you aren't left lacking support in labor.
Rest for 5 days after birth, no stairs, no carrying, no walks, not on your feet except to go to the bathroom or go to meals. Use a portable potty and a futon if you have to. Have prepared meals, friends bring food, etc.
Rest from day 6-14 in the home avoiding stairs except if you live on a multifloor home and need to use the stairs to go to the bathroom or to be with the family. Then down once and up once a day. Use a portable potty chair the rest of the time. Take your first outing at the end of this time, or in the second week. If you have to see the doctor before then, take a nap immediately afterwards and get help with meals that day.
Days 15-45 one errand a week, one visit a week to a parenting group or other place of support. No cleaning other than a short visit to the kitchen sink. No vacuuming or picking things up off the floor or carrying anything heavier than baby. Have someone else carry the car seat and carry baby in a sling, not the car seat of a baby carrier seat.
Continue at that time with yoga and pelvic floor balancing and strengthening most days (plan everyday and see if you can get in at least 5 days a week).
That's what's on the top of my head.
Whole Woman, Inc. has an article on Preventing Maternal Injury During Birth. You may find some more tips.
The Childbirth Connection has several articles on Preventing Pelvic Floor Injury and Dysfunction.