Copper in the uterus.

Copper-releasing IUDs seem to have a greater antifertility effect due to their continuous releasing of copper. This release results from an interaction between the copper and uterine secretions. Several agents in the uterine secretions, the amount of surface area of the copper, and the quantity of the solvent all influence the copper release rate. Microscopic photographs illustrate the progress of copper corrosion. The process of corrosion involves the replacement of copper atoms by other atoms from the uterine secretions on the corroded areas. Only a cross-sectional picture of the wire will indicate the amount of corrosion which has occurred. The corrosion occurs in variable locations, indicating that increasing the wire dimensions will not increase the lifetime of the devices. Studies with a copper IUD having a noncorrodable silver core--the Nova T--have shown this device to have significantly lower pregnancy rates than the Copper T 200 and a functional lifetime of up to 5 years.