Reply #147: correct about mechanism

[LisaLL]

"Their primary method is to make the uterus unfriendly toward contraception - they keep the egg and sperm from meeting. Keeping a fertilized egg from implanting *might be* a secondary method"


Thanks, gollygee. Primary method is to prevent fertilization.
No matter what the data shows, some people will continue to falsely
say that the primary mech of IUDs is to prevent implantation.

Paraphrased and quoted:
IUDs work primarily by preventing sperm from fertilizing ova. The copper IUD increases uterine and tubal fluids containing copper, ions, macrophages etc that impair sperm function and prevent fertilization. The progestin IUD has many mechanisms including thickening of the cervical mucus, inhibiting sperm capacitation, suppressing the endometrium, etc.

Two areas of evidence support that IUDs work earlier than originally thought. One is by the use of sensitive pregnancy tests which do not reveal chemical pregnancies occurring. Also, there have been studies in women having their tubes tied mid-cycle. At the time of surgery, the fallopian tubes were flushed and the fluid examined under a microscope.In women not using contraception--they found fertilized eggs in about half. In women using IUDs no fertilized, normally dividing eggs were recovered.

(Source: Contraceptive Tchnology 18th revised edition. Chapter 21 by D Grimes)