I am considering using an IUD. My doctor gave me pamphlets on a copper T-shaped IUD. I had always heard that the IUD prevented implantation of a fertilized egg. He said that new research indicates that the copper interferes with sperm motility, which prevents the sperm from ever reaching the egg. How exactly does the copper do that? Like many women I know, my only major objection to the IUD was that it prevented a viable fertilized egg from implanting. If what my doctor said is true, this will open up the use of IUDs to many women.

S.C.

While an IUD will indeed prevent the implantation of a fertilized egg, its primary method of action is preventing fertilization in the first place. The copper causes an inflammatory response in the uterine cavity. This prompts an influx of white blood cells that attack sperm. The white blood cells release chemicals that interfere with tubal motility, sperm motility and the sperm activation required before fertilization.

Although blocking fertilization rather than preventing implantation is considered the mechanism of action, IUDs may still be unacceptable to women who consider blocking implantation analogous to abortion.