UN Population Division, Department of Economic and Social Affairs,
with support from the UN Population Fund (UNFPA)

IUDs Block Fertilization


Intrauterine Devices

Family Health International, Vol. 16, No. 2, Winter 1996

Copyright 1996, Family Health International

IUDs Block Fertilization

Intrauterine devices (IUDs) achieve their primary contraceptive

effect by interfering with sperm motility and survival to prevent

fertilization. In rare cases, when fertilization does occur, IUDs

may also prevent implantation.

Any IUD prompts an endometrial reaction that promotes the release

of leukocytes and locally-acting substances, called prostaglandins.

These act simultaneously in the cervix, uterine cavity and oviduct

to impede sperm from fertilizing the egg. The copper present in

copper IUDs also has spermicidal effects.

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/

Research teams in Chile and the Dominican Republic have concluded

that fertilization is interrupted by IUDs through multiple actions

not completely understood. A Chilean research team searched for ova

by flushing the uterus on the second through the fifth day after

ovulation. Fertilized eggs were found in eight of 36 women using no

contraceptives, while only one fertilized egg was recovered among

22 users of inert IUDs that contain no copper and none in 43 users

of copper IUDs.3/  In the Dominican Republic, a comparison of copper

IUD users and women using no contraception showed that none of the

eggs from copper IUD users were fertilized, in contrast to more

than half of the eggs recovered from noncontraceptive users.4/  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


1. 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.

2. Ortiz ME, Croxatto HB. The mode of action of IUDs. Contraception

1987; 36(1):44.

3. Ortiz, 55.

4. 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.

5. 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


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