Evolution has divided the reproductive role between two parties for the sake of survivability of the species, not as a sop to the mau-mauing of feminists. A child isn't some trinket of a woman's simply because she is gestating it, the child is the product of a biological union. Her pregnancy is her duty as an organism. We forget that reproduction is the primary purpose of life.
That a particular human organ or capacity was adaptive, within the evolutionary environment, does not demonstrate that it places any moral obligation on the individual.
IUDs prevent pregnancy, in part, because the foreign body inside the uterus irritates the lining and wall making it hard for an embryo to implant
. The IUD functions successfully when it causes abortion to occur. An IUD user may effectively have numerous abortions, over the years. (As a critic of anti-abortionist ideology, I regard this as a poor reason to foreswear the IUD.)
The next time you run into a strong anti-abortionist, ask if IUDs should remain legal--and if so, why.