Smart - sweetheart - I somehow doubt there is any correlation at all.
In the vast majority of cases a pregnancy, carrying 10-15lbs or so of baby, placenta and amniotic fluid (and sundries) for the last month or so followed by pushing said baby (with a cranial circumference of 13 to 15 inches) through the birth canal, does not weaken the pelvic floor muscles enough to cause prolapse. I sincerely doubt that a cock, even with a circumference of 6 or 7 inches, is going to dent that
Seriously - cunts were designed for fucking and uteruses were designed for bearing children, both are remarkably robust and the prolapsed uterus is far more likely to result from hormonal issues than physical ones. The cervix and various supporting muscles of the pelvic floor protect the uterus very well during sex. I'm guessing now, but I'd say prolapse where there is no hormonal deficiency is likely to be a genetic predisposition.
Have a read of this, The Female Internal Genital Organs
, and follow the link to the 'pelvic floor'.