Assessment of olefin-based IUD tail strings.

The "tail string" that extends from a contraceptive intrauterine device (IUD) into the vagina is an illustrative case in materials engineering design. The strings must satisfy certain criteria for strength and other properties in order to fulfill the function of providing a means of insuring that the IUD has not been ejected, and eventually of helping remove the IUD. This must be done without contributing to an additional risk of unwanted medical side effects beyond those that may be inherent in any such device. Oriented monofilament olefins appear to satisfy these criteria, and have been used successfully in several IUD designs. This article describes a study of two such monofilaments taken from new IUDs, showing how the material's processing, structure, and properties lead to effective performance as tail strings. Several types of used IUDs were also studied, to insure that nothing occurred during use that would alter the conclusions drawn from the study of new strings.