Intrauterine Devices: Separating Fact From Fallacy

, Magee-Womens Hospital, University of Pittsburgh School of Medicine

In This Article

Mechanism of Action

The "mythologic" mechanism of the IUD is the creation of an inflammatory reaction in the endometrial cavity that prevents or disrupts the implantation of a fertilized egg. Research has proven this to be untrue; the IUD acts primarily as a contraceptive device by preventing fertilization. Copper-containing IUDs release free copper and copper salts without any measurable increase in serum copper levels. In fact, the amount of copper released daily is less than the average daily intake in a normal diet.[2] The resulting changes in the intrauterine environment and cervical mucus act to immobilize sperm or prevent their migration to the fallopian tubes.[3] Using highly sensitive serum assays for [[beta]]-HCG, evidence of actual fertilization was found in only 1/137 cycles (0.7%) of women using a copper-containing IUD.[4,5] The copper IUD also appears to directly affect oocytes, perhaps lessening or inhibiting their ability to be fertilized.[3,6] This would help to explain why the copper IUD also protects against ectopic pregnancy. Progesterone-containing IUDs, on the other hand, cause a decidualization of the endometrium, leading to atrophy of the glands and thickening of the cervical mucus, creating a barrier to sperm penetration.


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