Preventing pregnancy with the cervical cap

Science News, August 12, 1989 by K.A. Fackelmann

Preventing pregnancy with the cervical cap

Near-perfect use of the cervical cap carries a first-year pregnancy risk of 6 percent -- half the risk posed by typical use of the cap, say researchers who have completed the largest clinical trial to date of the recently introduced birth control device.

"This is one of the first studies to look at the relationship between the style and type of use of a [contraceptive] method and [its] effectiveness," says Gary A. Richwald of the School of Public Health at the University of California, Los Angeles. He and his colleagues studied 3,433 women fitted with a cervical cap -- a rubber cup about 3.5 centimeters in diameter, held in place over the cervix by suction and carrying a film of spermicide. Their report appears in the August OBSTETRICS AND GYNECOLOGY.

The Food and Drug Administration approved marketing of the cervical cap in May 1988 after a National Institutes of Health study and other reports demonstrated its effectiveness in preventing pregnancy. The NIH study randomly assigned 1,529 women to a cervical cap or diaphragm, finding overall first-year failure rates of 17.4 percent for the cervical cap and 16.7 percent for the diaphragm. But these rates included statistics on typical users, who may occasionally forget to use the cap or spermicide. Richwald's study shows that near-perfect users -- women who never have sex without the device, use spermicide 100 percent of the time and wear the cervical cap no longer than 72 hours -- have a much lower risk of unintended pregnancy than the overall average reported by NIH.

Richwald's team found no serious medical complications with the cervical cap, although more than 20 percent of the women in their study reported cap dislodgement during or after intercourse. Some women discontinued its use for this reason, although Richwald says dislodgement shouldn't contribute much to pregnancy risk because the cap works by delivering a spermicide dose near the cervix.

The cervical cap is an effective and convenient birth control method, comments Cynthia Pearson of the National Women's Health Network in Washington, D.C. But she adds that more research must determine whether the device boosts a woman's risk of cervical cancer. The NIH study hinted that cap users, compared with diaphragm users, may have a greater chance of developing cervical cancer, but Richwald's study found relatively few cap users with abnormal Pap smears indicating cervical cancer risk. Still, FDA advises cap users to get a Pap smear after the first three months of use, while an ongoing postmarketing study attempts to assess any potential cancer risk.