Biomaterials in Obstetrics and Gynecology - Biomaterials Science: An Integrated Clinical and Engineering Approach - page 151

legend, the first IUD users were desert caravan drivers who used intrauter-
ine stones to protect their female camels from pregnancy [3]. This story,
despite being not well documented, is a demonstration of an early use of
biomaterials as a contraceptive method. In 1909, Richter reported his experi-
ence with a silkworm catgut ring with coils of nickel and bronze [4]. This
preliminary IUD was the base of the 1930s Grafenberg ring, made of coiled
silver and gold.
Modern IUDs include the copper IUD and progesterone (or levonorg-
estrel LNG)-eluding IUDs (Mirena ® ).
The copper IUD is made of a plastic stem and arms, and is covered with
coiled copper. The TCu380A IUD (Paragard ® ), currently approved by the
Food and Drug Administration, is widely used in the United States. This
IUD creates a copper surface area of 300 mm 2 in the vertical arm and 40 mm 2
on each of the transverse arms. The lifespan of this IUD is at least 10 years,
with reported efficacy even after 12 years of use.
Mechanism of action of the copper IUD is the release of copper ions into
the endometrium. This creates a local inflammatory response. There is a dra-
matic increase in endometrial leukocyte count with local secretion of inflam-
matory cytokines. Pregnancy is prevented mainly by the spermicidal effect
of this inflammatory process. In addition to phagocytosis by endometrial
macrophages, some of the products of these leukocytes create a toxic envi-
ronment to the spermatozoa. Additionally, copper has the ability to impede
sperm transport through the cervical mucous and sperm viability. A third
mechanism of action is debatable: it has been claimed that the environment
around the IUD may be hostile also to the blastocyte, thus interfering with
early embryo implantation.
The LNG-releasing IUD (Mirena ® ) was approved by the FDA in 2000. This
T-shaped device contains a reservoir of LNG on its vertical arm. LNG is a
progestin (a synthetic derivative of testosterone that activates progesterone
receptors) that is released at a rate of 20 micrograms per 24 hours by this
intrauterine system. It acts directly on the endometrium, interfering with
the endometrial maturation required for implantation. In addition, it has an
inhibitory effect on ovulation as well as an effect of thickening the cervical
mucous. The inhibitory effect on endometrial maturation is responsible for a
significant reduction in menstrual blood flow and dysmenorrhea (pain with
menstruation). Indeed, Mirena ® was approved by the FDA in 2009 for the
indication of heavy menstrual bleeding. It reduces menstrual blood loss by
90% one year after insertion.
Both the copper IUD and the LNG-releasing IUD have excellent efficacy,
with a 5-year pregnancy rate of only 1.4% for the TCu380A IUD and 0.7% for
the Mirena ® .
When comparing efficacy of contraceptive devices, one must take into
consideration that there is a difference between “typical failure rate” and
“perfect failure rates.” For example, if a couple is relying on condoms for
contraception, the typical failure rate will be higher than the perfect rate,