The wombs would come from dead donors, just as most other organs do, and would be removed after the recipient gives birth so she would not need anti-rejection drugs her whole life. To read on...
We've blogged about this before -- but two big questions arise that no one seems to want to answer: What about the impact of anti-rejection drugs on the fetus during development? From what I understand, anti-rejection drugs are teratogenic or embryocidal. Does a woman's desire to bear a child justifiably outweigh the likely harm to the fetus? And if you decide that a woman could justifiably exercise her autonomy in such a manner, why not allow male pregnancy? (which we've blogged about before, too, here and here.) Either through a womb transplant or via an embryo implanted in the peritoneal sac? (some sort of flexible mesh that would allow growth of the embryo/fetus and yet prevent the endometrial and placental tissues from attaching to major organs would have to be devised).
I could imagine some argument about this being a women's natural role, but pu-leeze, do we really want to go there?
(image courtesy of http://www.malepregnancy.com -- an artist's rendition)