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Intrauterine devices (IUDs) achieve their primary contraceptive effect by interfering
with sperm motility and survival. They also prevent fertilization and, in rare cases,
implantation.
Any IUD prompts an endometrial reaction that promotes the release of leukocytes and
locally-acting substances, called prostaglandins. These act simultaneously in the oviduct,
cervix, uterine cavity and genital tract to impede sperm and egg development.
The presence of copper enhances this effect. Studies among women using copper IUDs have
shown a reduced number of live sperm after intercourse when compared with nonusers. The
interruption of sperm migration begins in the cervical mucus and continues in the uterus
and oviducts. A California research team compared eight  women
15 to 30 minutes after insemination. Sperm were detected in the oviducts of all four women
not using IUDs, while no sperm were in the oviducts of copper IUD users.1
Many studies have shown copper to act as a spermicide. In a study of the Copper T 200,
scientists observed that the sperm heads were detached from the tails in a majority of
sperm cells.2
Fertilization is also interrupted through action on unfertilized eggs. A Chilean research
team found few eggs in the tubes and uteruses of IUD-using women. They searched for ova by
flushing the uterus on the second through the fifth day after ovulation. Eggs were found
in one-third of 36 women using no contraceptives, while only one egg was recovered among
22 users of inert IUDs that contain no copper and none in 43 users of copper IUDs.3 A comparison of copper IUD users and women using no
contraception showed that none of the eggs from copper IUD users were fully developed or
fertilized, in contrast to more than half of the eggs recovered from noncontraceptive
users.4 Other data show the copper IUD slows the development
and transportation of eggs. When screened for a hormone secreted just prior to
implantation of a fertilized egg, one study found few IUD users who tested positive for
the hormone. The study concluded that the IUD's prevention of implantation is very rare.5
FHI trials of 10,000 women in 23 countries conclude the annual pregnancy rate for the
Copper T 380 is very low, 0.5 per 100 women (one pregnancy among 200 users). Copper
accounts for this high degree of contraceptive efficacy, according to Irving Sivin, senior
scientist at the Population Council, which developed the Copper T 380. "With the
inert IUD, we know that sperm transport is interfered with," says Sivin. "But
with copper, it is interfered with more. And the more copper, the more interruption."
Copper IUDs also function well as emergency contraception when inserted within five days
after unprotected intercourse. Emergency contraception is used after unprotected coitus to
avoid pregnancy.
-- Sarah Keller
Footnotes
- Tredway DR, Umezaki CU, Mishell DR, et al. Effect of
intrauterine devices on sperm transport in the human being: Preliminary report. Am J Ob
Gyn 1975;123(7):734.
- Ortiz ME, Croxatto HB. The mode of action of IUDs.
Contraception 1987; 36(1):44.
- Ortiz, 55.
- Alvarez F, Brache V, Fernandez E, et al. New insights on
the mode of action of intrauterine contraceptive devices in women. Fertil Steril
1988;49(5):768-73.
- Wilcox AJ, Weinberg CR, Armstrong EG, et al. Urinary
human chorionic gonadotropin among intrauterine device users: Detection with a highly
specific and sensitive assay. Fertil Steril 1987;47(2):265-70.
For more information, visit Family Health International's Website at www.fhi.org
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