[corkoman]

Not to quibble but the IUD was intended to prevent a conception not a birth.

You would need a much larger spring to do that - but then it would only oscillating a few times and then that baby would come flying out shouting Yahoo!!!

[Mrs. Don-o]

As the article says, the coil can sabotage procreation three ways:

• sometimes by thickening the cervical mucus so the sperm are immobilized
• sometimes by thinning the nutrient lining of the uterus so the young embryo can't implant
• sometimes by preventing ovulation.

The first and third are contraceptive. The second is abortifacient.

This is not exactly predictable. It will vary from cycle to cycle, depending on the woman's own varying hormonal levels.